New to this, Seems obvious he died?

So I just watched the LEMMiNO video, and I was hoping to get some clarification from the enthusiasts here.

Does the discovery of the $5,800 at Tina Bar not prove Cooper died when he jumped?

Maybe there is a detail that isn't mentioned in that video, but Cooper willingly disposing of a portion of the money seems ridiculous. The rubber bands breaking down or something seems like it could be prevented if it was packed in sand no? And Cooper putting it there for safe keeping or whatever seems insane because it's a beech.