Man...that is some scary action. I'm thinking this is a time that you may be up against a higher set and a made straight....you are potentially drawing totally dead. The best you can hope for honestly is to be up against a straight and a flush draw. Nobody left in the hand raised preflop so hands like 66 and 99 are likely here....as is 78.
All this being said...not sure i'm folding a set here. You are getting pretty decent odds to hit your full house.
If you are up against the straight and tptk
Result
http://twodimes.net/h/?z=1278405
pokenum -h 7h 8h - as 9c - 5h 5c -- 5s 6d 9s
Holdem Hi: 903 enumerated boards containing 9s 5s 6d
cards win %win lose %lose tie %tie EV
8h 7h 571 63.23 324 35.88 8 0.89 0.635
As 9c 55 6.09 840 93.02 8 0.89 0.064
5c 5h 269 29.79 626 69.32 8 0.89 0.301
If you are up against another set and a straight
Result
http://twodimes.net/h/?z=1278411
pokenum -h 7h 8h - 9h 9c - 5h 5c -- 5s 6d 9s
Holdem Hi: 903 enumerated boards containing 9s 5s 6d
cards win %win lose %lose tie %tie EV
8h 7h 640 70.87 254 28.13 9 1.00 0.712
9c 9h 213 23.59 681 75.42 9 1.00 0.239
5c 5h 41 4.54 853 94.46 9 1.00 0.049
if you are up against the straight and a flush draw
Result
http://twodimes.net/h/?z=1278413
pokenum -h 7h 8h - as ts - 5h 5c -- 5s 6d 9s
Holdem Hi: 903 enumerated boards containing 9s 5s 6d
cards win %win lose %lose tie %tie EV
8h 7h 348 38.54 555 61.46 0 0.00 0.385
As Ts 234 25.91 669 74.09 0 0.00 0.259
5c 5h 321 35.55 582 64.45 0 0.00 0.355
I'd say it's a fairly close call.....you are probably ahead some of the time, and the times you aren't ahead you are probably drawing live more times than you are drawing dead. If you are drawing live you are getting about the right odds to draw.