Only those altcoins are dieing that have no working product and no real world use cases. And these alts need to die as they are dirtying the whole crypto world. Yes new projects are going to come but only those with real development and use case is going to survive.
My point is in the 3.5 years or whatever other coins came out. These coins work just as well at getting sent around (changing ledger entries really). Some work even better in subjective terms, like confirmation speed, privacy, or low fees. The only thing bitcoin has over them is high hashrate which after a certain level is not any more beneficial. And it's all open source so even lousy altcoin developers can copy anything good developers come up with.