They can get plenty of data even if you only sleep a little bit. I think they like it if you sleep 5 hours or more, but it's okay if you can't. I had one sleep study where I only slept 3 1/2 or 4 hours, and they said that was fine.
Even if you end up not sleeping at all during your study, it's still worth doing for two reasons:
1) it could be that they'll get insight into the problem by studying what's going on when you're NOT able to sleep (i.e., you could be drifting and having microsleeps and then getting jolted awake, etc. or it could be that your brain never enters the "sleepy" stage needed to actually go deeper into sleep, etc.)
2) it could be that you ARE sleeping but aren't aware of it. I know that sounds

crazy, but a pretty good proportion of insomniacs, when they go for a sleep study, turn out to actually be sleeping a fair amount (maybe not enough, but some.) Then they'll wake up the next morning and claim they didn't sleep at all!!!
The reason this happens is that your consciousness is greatly altered even before you fall asleep, so you sometimes sort of don't remember sleeping (for some people, that is.) Or there's another disorder going on where you're not entering deep sleep, so it's not refreshing and you remember tossing and turning and feeling "wakeful" a lot (even though you were actually sleeping). Anyway, this issue can be exacerbated by stuff like Ambien, since it causes alterations in consciousness.
Bottom line: get it done. It can't hurt, and it may help.
P.S. have you asked about Trazodone? I mentioned it when replying to your last post -- I've had some success with it.