PER (75) wise this would be the greatest trio of ALL time. I'd hate to lose Noah but if you believe in PER, you gotta dig those numbers. Bron, Rose and Noah isn't bad, PER of 67.9 is still championship caliber.
http://www.realgm.com/src_feature_pieces/916/20100609/the_biggest_big_3/s/
The Bulls could alternately acquire Bosh in a sign-and-trade, but so far everything we've heard is that the front office would be unwilling to sacrifice Noah in the process. I would agree with the general premise of Noah being untouchable, but if the decision came down to a 'take it or leave it' where the Bulls for the next five years would either be LeBron, Rose and Bosh, or Joe Johnson, Rose and Noah, I think the answer should become very simplistic.
To make a rudimentary analogy, the below trio would essentially be taking Michael Jordan and Scottie Pippen, plus throwing in Gary Payton to play their entire primes together in the 1990s.
10-11 Bulls
LeBron: 31.2
Rose: 18.7
Bosh: 25.1
Total: 75.0