Just because said that, it doesn't mean it's true.
I don't think they held to the Big 3 for too long. Bird and McHale had huge injuries that hurted their games to the point they never were the same players.
If Bias was able to play in the 1986-87, I think McHale would have surgery and recover instead of playing on that broken foot. Also, Bias would have taken some minutes from Larry Legend, allowing him to rest more and MAYBE (you never know) Bird could have played a couple more seasons.
Of course, Bias might never become the MVP he was projected to be, but he would've been a contributor in any case, because of his length, athleticism and offensive game. In the 1984 game against UNC and Jordan, Bias was still 2 years away from the player the Celtics would have gotten, and he was automatic from 18-20 feet. In his last year in Maryland, Bias looked unstoppable on offense, and a beast on D.
Then, when you've survived 4 years of injuries to your best players, and the tragic loss of Bias, you have some young pieces to complement your HOFers. One of them, Reggie Lewis, starts to dominate and look like the second best SG in the NBA. And one day you find out that not only Bird isn't coming through that door, but neither Reggie.
I became a Celtics fan in 1985, after watching them losing to Kareem (and Magic). The next season I was happy to see them win it all, and when I found out they've drafted Bias, I was excited. Then, tragedy and a feeling of what could have been. That set a pessimistic tone, with injuries and the sensation that everything went wrong. When Reggie was hurt against Charlotte, I thought of Bias, and even when I hoped Reggie would be back and playing at 100%, I was scared he could end like Len. Then, it happened, and that was like a dejà vu, but exponentially worse. As a Celtic fan from abroad, with little NBA coverage in 1993, and even less in 1986, I can tell those were the worse moments for the best club in basketball.
It took a lot to recover from those tragedies and the Pitino Disaster, but the Celtics were able to come back thanks to Pierce, Garnett, Allen and the rest. That's the reason why we should thank the 2007-2008 and beyond Celtic teams. And yes, if it was the Lakers or the Knicks, I'm sure Herr Stern would've found a way to help them.