A fact that most people miss is that an invincible dvd is useless if there's nothing to play it. The question is, if you can get your dvds to last 50-100 years, will there be a dvd player and compatible display around to play them in? Take for instance the early cylindrical phonographs (if there's a real name for them, I don't know it). My grandfather has some, they've lasted a very very long time, but the problem is that the player didn't hold up so well. Remember, this is with an analog signal, so you don't have to deal with different formats. Playing back an analog signal from a record is a whole lot easier than resurrecting an "ancient" digital one. Do you have an 8 inch floppy drive?
While dvd players could be manufactured again in the future, just as cylindrical phonograph players sometimes are, I think it's worth mentioning that you'll need to have a reader as well as the media.