I'm no expert on the matter
but a friend of ours has 1300ac out toward Brackettville, they released some bred stocker does on their place this year. they just released them flat out. no preparation like what was described above. those deer are having a hard time. I haven't heard that he's lost any of them yet. but he sends me game cam pics sometimes...and those girls look pretty poor. they look sick compared to the native deer. I suppose they will rebound...I dunno. but under those conditions I'd bet whatever fawn they bore also isn't looking at the best survival rate either.
This situation is true for a lot of animals that have been pen-raised or at least raised on a feeder their whole lives. They've never learned to rustle. We do a ram test every year to determine growth rates, etc, and the second those rams come off the feed they'll drop about 30 pounds.
Usually they'll adapt but it may take a year or so. The key is if they raised offspring, those fawns won't be pen-raised and should be good stock going forward.