One example is that BTC's transactions costs are getting more expensive as time goes on. They were supposed to start going down after the most recent hard fork, but I don't know if has been the case.

Another example is that the electricity cost to run the system is going up at an unsustainable pace. Eventually they'll have to switch to an new way to propagate the blockchain something other than Proof of Work mining.

Most likely though, these problems will be solved with some kind of hard fork rather than BTC dying.