Happened to me. Or well, my wife.

I've been playing on and off for a bit. So my account got converted. I tried to do the same to her account but got an error, but since she wasn't really playing I decided I'd try again later. Well, guess who simply forgot and tried logging in recently? Something I bought and still is being sold is suddenly just gone. Great.

It was a minecraft account, then mojang and now you'd need a Microsoft account..

If you want to play on a server with friends, you need to disable account verification on that in order to allow non-logged in players to access it. So, possible. But not always practical.