I doubt it'll be replaced. The most I'm guessing that will happen would be inflation in the market, and some other cryptocurrency rise above the value of bitcoins for the time being, but bitcoins would still take 1st place on the average in terms of value
The future is certainly beyond our control, time will come and if that happens I believe Ethereum will take place as the top Altcoins to replace bitcoin as IMO it's the most population altcoin now. I even invest now since the price is very low and I have witnessed it has gone up
BTC0.03 +.
Ethereum is a clear opposite of bitcoin, as when the price of bitcoin increases ETH drops, so the failure of bitcoin will be its success.