[BillyCoxDodgers3B]

As Mike said, I think it will be fine.

Remove all four screws, then turn the case so that the card is facing down before trying to remove the back piece. Then, see if it's stuck to the front piece. If it is, put it in the freezer for an hour or two before seeing if that has helped free it up (it should).

I'm guessing your friend knew to let the signature dry before putting it in the screw down, so all should be well unless he's had it in all kinds of strange temperature fluctuations/humidity over the last 30 years. Even if so, it might be fine.

If the ink has somehow stuck to the front piece, I don't really know of any way of removing it without incurring some issue(s). What do others think? I'm personally more used to buying unsigned cards in these holders for the purpose of getting signed after they've been removed. Haven't encountered a stuck one yet, thankfully.