It all depends on if the IP owners can keep the IP relevant. I mean Superman and Batman are closer to 100 years old than 50 years old. If you had told someone back in the late 30s that Superman and Batman in funny books would still be popular, if not more so, in 100 years they would probably think you need to be in the sanitarium. Then other older, or similarly aged, properties have different levels of popularity. From practically nothing like say Tin-Tin (no shade) to Disney's mainstays (Mickey, Donald, etc.).
I think some of the Gen-X properties are starting to hit that imaginary bump that I have in my mind where they have now been around long enough that momentum could be on their side for longer staying power in the cultural zeitgeist. I think that is around the 50 year mark. I mean GI Joe and Barbie are over 60 years old, Star Trek is just turning 60, Star Wars is almost 50 and then you get into the 80s properties like Transformers, He-Man, etc. and they are closing in on that imaginary bump in my mind. Obviously Transformers and Star Wars are much more popular than say GI Joe or He-Man, but both Barbie, and now He-Man are coming back in the larger media landscape thanks to big movies (hopefully for He-Man).
I think once a property passes 50 years, with some continued (relevant) cultural presence, it has a good chance of staying around for longer than we could know. I mean 50 years gives you what? 3 generations of exposure? That probably has some cultural "seepage" that gets into the larger population. Granted, as I said, it also depends on how relevant it can stay with popular media awareness.
When it comes to toys (especially action figures) that is tougher because much like a lot of physical media, the audience seems to be shrinking in favour of digital and I don't see a good way to counter that trend.