Will another coin beat bitcoin in terms of total market cap? Maybe, maybe not. Is it possible? Very possible. Though Ethereum is slowly but surely closing up on market cap(currently a 57.3 billion difference[1]), it still has a far far way to go; and I honestly don't see bitcoin being replaced soon. Probably in the future, but who knows? Too early to tell. And it might not even be ETH.
[1]
https://coinmarketcap.com/I see that it can, ethereum was the 2nd top coin in the world of currency but when we see that the price was a huge average of bitcoin to ethereum. The market flow of ethereum was better than bitcoin because there are too many believers and users of ethereum when they join at the crypto. I think future can reach by ethereum when the total supply was fix.