Thankfully, I forget the details[0]. From experience, no, it won't be exactly hosed: you'll end up with a .nfs004950384672385721380937 file that will grow and eventually fill up the partition... nothing an rm -rf / won't fix. And then there's negative cookies and stale mounts that require a rebooton most unices I've seen... you had to remind me, didn't you?
from my own limited experience, stale mounts are not a problem if you can unmount then mount again the partition containing the "damaged" export. Note that mount -o remount doesnt do the trick, but umount then mount does it. That's why i keep nfs mounts on separate partition. (i have 4 X kernel-over-ftfp and root-over-nfs boxen that users can start and restart at will without proper shutdown, and a reboot each time a stale mount occured started to get on my nerves.)