What will happen to the Iphone/Ipad Apps we bought in ten or fifteen years?

After purchasing many apps on my Iphone, I’m wondering if they will continue upgrading into perpetuity, or if there is an end in sight for app relevance?

If not are the apps just going to evolve like other programs, and will my original purchase price always keep me locked in for free upgrades? Maybe this is written in the fine print of my user agreement somewhere, but I must have missed it (aka didn’t read it, and might have signed away my soul to Apple).