So the former will eventually be able to be brute-forced in coming decades when quantum computers can be accessed. But the lost keys are lost forever.
Brute forcing keys will never a thing on BTC. If it ever does, the network will do a hard fork and change its algorithm to protect itself.
I doubt that quantum computers will possess a threat to btc. If it ever does, unless you own hundreds of bitcoins, it will be the last thing you'll worry about.