It is definitely here to stay, but it won't replace Bitcoin. It has a different functionality.
I'm currently viewing Ethereum as a safer investment than Bitcoin. Ethereum has a leg to stand on because there are thousands of other tokens built on top of its blockchain platform. But the value of Bitcoin is based solely on trust in the system. If people start to lose trust in Bitcoin's real intrinsic value, the price will drop. But Ethereum has a greater intrinsic value due to its functionality.
You have really said it all. Bitcoin is based on trust and been the first protocol it has fundamental features that are distinct from ethereum protocol. Talking about replacement is out of place. I thinks what we should talking about is functionality issues.