i have messed around with those file un-delete programs before.
some files come back okay, some are corrupted and wont come back.
if you use one of them programs, the dvd might be corrupted in some spots.
how much corruption is unknown.. and maybe you are willing to deal with that corruption, but the un-delete program is telling you no.
that is when you take the hard drive to a specialist to have them recover the deleted dvd.
you might see things like audio stuttering or video artifacts.. audio artifacts are digital noises or moments of silence and such.
it might be worth it if the video was important.