I'm currently using equipment that's working perfectly well running on NiCads and solar panels that are only a little younger than I am. I expect in another 50 years they'll be a bit on the tired side, but it won't be my problem.
It won't be your problem but I'd expect whoever inherits it from you to still be able to get between 20 and 30% or so of the original capacity out of it. Which is likely ample to run simple stuff, assuming the simple stuff itself survives that long.