It wouldn't be terrible, but it wouldn't be good either.
The rule of thumb in the NBA is to never trade a star for depth (i.e. a few good players). In the NBA, your stars can play 40 mpg, having depth isn't really all that much of a luxury like it is in baseball, football, and hockey.
Now, obviously things would be different here. Trading Ray at this point would be more or less waving the white flag and moving toward rebuilding.
Here's the problem though, none of the players you mentioned are really building blocks for the future. Worse, Gibson and Brewer's contract goes one year beyond Ray's, and Asik would require a qualifying offer if we didn't want him to walk after this season.
What does all of this mean? It means that arguably the most valuable part of Ray's contract (the 10 million dollars it will clear when it expires) won't happen.
Instead, we're stuck paying nearly 10 million to 3 role players, rather trying to spend that on a mega free agent in the summer of 2012.
Now, could we simply let Brewer, Gibson, and Asik walk after the 2012-2013 season and spend their money in 2013? Sure, however, what's the point in doing that when we can just hold onto Ray and get it a year earlier?
Plus, we'd have people always asking the question, what if? if we didn't give the Big Three at least one more shot in the playoffs.
It's worth blowing that final chance for major building blocks. But it's not worth it for 3 role players who hinder our cap flexibility.
The simple fact of the matter is that with Ray and KG, the most valuable way the C's can utilize them for the future is likely to let them expire. It's very unlikely any team is going to give a future star for either of them. And if a team isn't willing to do that, it's not worth acquiring role players whose salaries add up either KG's or Ray's and destroying all future cap flexibility.