Rondo.

Even after the great wave of bittersweet sentiment over what Doc Rivers and the Big Three brought to Boston and how they left subsides to a more even tide of long-term expectations, the one word remains inescapable.

Rondo.

We all knew the day would come when Ray Allen would leave the Celtics and that came last year in a free agent signing with the Heat that left Ray with his unfair share of vitriol from too many Celtics fans. Doc expressing his disappointment in Allen and Kevin Garnett saying he lost Ray’s telephone number when he headed to South Beach didn’t help matters.

Allen, who demonstrated against the Spurs in a Game 6 for the ages that he had one more trick in his bag of three-point tricks, awaits the delivery of his second NBA championship ring now. And with Doc catching the last train for the Coast earlier in the week, I think we can agree the idea of forever Celtic loyalty was a bloated one.

We all knew the day would come when Paul Pierce and KG would leave and it came in a sudden, cold slap of reality Thursday night with a blockbuster trade with the Nets. No sooner had the Celtics drafted a 6-foot-11 long-hair from Gonzaga named Kelly Olynyk, who looks like he hung with Country Joe and the Fish at Woodstock, than Danny Ainge heeded his own advice and dealt two cornerstones of the Celtics return to glory before the franchise began to smell of dead fish. Two cornerstones who, incidentally, are nearly old enough to have been at Max Yasgur’s farm.

Ainge had once unsuccessfully urged Red Auerbach to deal Larry Bird and Kevin McHale when they still had significant value. In position of Red’s power many years later, Ainge, daring, savvy and sufficiently cold, wasn’t going to wait until his aging superstars had no value.

After the drama involving Rivers going to the Clippers dragged on for days, Ainge clearly wasn’t going to allow this deal to drag, too. The Great Experiment that many expected to last three or four years and lasted six was over within hours.

And when it was over, we can make a strong argument the Nets have taken a much bigger risk than the Celtics. We even say it was a layup, except for one word.

Rondo.

Look, there is a lot of pain for Boston fans this week. The Blackhawks score twice in the final 76 seconds to win a Stanley Cup that only a few days earlier seemed destined for the Bruins. Aaron Hernandez, who figured to be a star in Foxboro for years, instead finds himself in jail without bail facing murder charges. And now the Celtics have hit the big, emotional reset button.

Nobody wanted to win more than KG. When praising an athlete, coaches and pundits love to say “He made players around him better.” Well, KG made players around him braver. With an undeniable fire and force of will, he put backbone in a team. And in the end a spiritual strength is as meaningful to a championship as the X’s and O’s.

Over 15 years we watched Pierce score nearly 25,000 points in a Celtics uniform. More than that, we watched him grow from a young punk and drama queen to a certifiable champion. Few players could slow a game and quicken a fan’s heart more than Pierce with the basketball and 10 seconds left on the clock.

We listened as Doc charmed our socks off. We watched as he coerced his guys to play their socks off. He had everyone believing in Ubuntu: “I am what I am because of who we all are.” He took the Celtics to their 17th NBA title in 2008, came within one game of doing the same in 2010 and another game of returning to the Finals in 2012. Unfortunately, not even Ubuntu gives even someone like Rivers, who developed such a reservoir of good will, a free pass from criticism.

Bill Simmons of ESPN is catching lots of heat from Rivers and his son Jeremiah for saying Doc quit on the Celtics. While we can quibble over the “Q” word and Doc and Danny can bend over backward saying how much they love each other, c’mon, does anybody really believe Rivers wanted to continue coaching a franchise facing such a massive rebuilding job? Doc overstated his allegiance when he signed the five-year, $35 million deal in 2011. We shouldn’t make the same mistake now. He clearly relishes the idea of starting over with a strong Clippers team.

And Doc can get 3,000 miles away from that one word.

Rondo.

Getting four first-round picks, Ainge about maximized what he could get for KG, Pierce and Doc. Granted, some of the picks figure to be toward the back end of the first round, but the Celtics now have nine first-round picks in the next five years.

Remember that famous Rick Pitino quote about how Bird, McHale and Parish aren’t walking through that door? Well, Pierce, at 35, and Garnett, at 37, are going through that Nets’ door on walkers. Still, with Brook Lopez, Deron Williams, Joe Johnson, Pierce and Garnett’s leadership at power forward, the Nets are going to be very good — although there might not be enough basketballs to go around. That’s for rookie coach Jason Kidd, who was the ultimate distributor as a player, to figure out. The Heat are still the team to beat in the East. The Pacers and the Bulls, with a healthy Derrick Rose, are there with the Nets. This isn’t Russian roulette, but make no mistake, owner Mikhail Prokhorov is spending millions and millions on payroll and luxury tax for a one-time — at best two-time — shot.

According to multiple outlets the deal, which cannot be announced until July 10 because of the Celtics’ team option on Pierce, looks like this: First-round picks in 2014, 2016 and 2018 along with Kris Humphries, Gerald Wallace, Kris Joseph, MarShon Brooks and a sign-and-trade Keith Bogans for Pierce, Garnett and Jason Terry. Taking on $30 million over three years for Wallace is certainly not something Ainge wants, but it had to happen to make the deal work. Chris Mannix of Sports Illustrated, meanwhile, has reported Humphries might never play for the Celtics and could be dealt to Charlotte for UConn’s Ben Gordon. Fascinating.

In the meantime, there’s every indication Ainge has invested in Rondo as the centerpiece of his franchise. The Celtics didn’t go after a point guard in a point guard-rich draft. That’s one indication.

Yet so many questions remain.

How will his surgically repaired knee, which knocked him out last season, hold up? Can Rondo return at his frightening speed? How will he handle playing on what figures to be a bad team? As the best player, how will he carry the leadership without the guidance of Garnett? Will Rondo remain distant and moody? This is a guy who has run afoul of Rivers, Allen, etc. Rondo is an incredible playmaker, but he doesn’t figure to easily fit as the No. 1 scoring option. And if he does, how will it sit with him that he is essentially underpaid? Would he listen to a young coach like Jay Larranaga? Or will Ainge figure it better to bring in a tougher, more mature voice like Stan Van Gundy?

And here’s something to think about. If a Rondo-lead team with Jeff Green, Avery Bradley, Brandon Bass and Jared Sullinger do figure out a way to win more games than expected, does that actually hurt the plan to be bad enough to land a top lottery pick like Andrew Wiggins, Jabari Parker, Marcus Smart or the Harrison twins?

When the hurt wears off, banners will be raised at TD Garden to honor some great Celtics. In the meantime, Ainge has given himself the building blocks, time and cap space to do what everyone knew he’d have to do one day. Now, he wonders.

Rondo.