As far as I know, there's no crack/backdoor for Filevault/encrypted disk images, so the data should be safe (as long as you use a good password that can't be easily cracked and is not on a sticky note on the bottom of the MPA).
Actually there are several ways someone could "crack" a FileVault. The very least thing you should do is activate encrypted virtual memory (because your login password can end up in the virtual memory and is very easy to find there) and deactivate safe sleep (because it writes all the memory contents to the disk). But as far as I know, even if you disable safe sleep it will be used automatically when your battery runs empty (maybe someone can clarify that point?).