I personally would NOT do that, as Apple and the individual companies that own/develop the apps have the right to remove apps from the store AT ANY TIME they choose.
Meaning, that app you still find useful, yet is not in the store anymore, won't be able to be gotten back.
The same is true for all media (music/movies/podcasts/etc.) — just last week Disney unexpectedly removed content people had paid for (some controversy about what was/is going on with that). But they're far from the only ones to do such things.
Protect yourself by keeping copies. Why I keep a copy of everything on my Mac Mini (I use it as a centralised server type of thing: all iTunes, all Plex, all my docs, available all the time), using some decent Tbolt external storage (and backed-up properly). Saves me the bother of problems all the time.
But do what's best for you, of course.