What do you mean "game over"?

The BTC passed the USD 1000 mark not so long ago. I do consider it possible that we'll get under USD 1000 again within a year, but that's still not "game over"! Far from it!

I do find it likely that some other crypto will overtake Bitcoin at some point. That would mark the beginning of the end for Bitcoin - but still, I believe some people would be trading Bitcoin even decades after that happens.

My worst fear is that some major constellation of banks will launch some kind of "electronic money", promote it as "better than bitcoin" and launch some massive campaigns. Some easy-to-use banking-backed coin with some few of the attribute of cryptos, but missing essential things like decentralization and permissionlessness may really get kickstarted to become far more popular than Bitcoin. For me, that will be the end of crypto as we know it. But still not really "game over", there will still be a niche for the current cryptocurrencies. The market cap will just reflect that those crypto currencies does not have the potential to become the standard for electronic payment rails. Bitcoin will become a bit like PGP or IRC, considered "old-tech", not used by the masses, but still in use.