I really don't expect to be asked to pay again. I paid once, years ago when it was in beta. I have an account, it should stay that way. It would be really unfair if they were to ask us to pay again.
I'm not too worried about Minecraft for Windows. But, they might decide to drop support for the Mac or Linux versions. That would be pretty lame. On the other hand, look at Skype. It's still supported across all the platforms it used to, before it was bought.
The core of Minecraft is, has always been and will always be the community. Microsoft probably know it. I hope they do!
I'm not too worried about Minecraft for Windows. But, they might decide to drop support for the Mac or Linux versions. That would be pretty lame. On the other hand, look at Skype. It's still supported across all the platforms it used to, before it was bought.
The core of Minecraft is, has always been and will always be the community. Microsoft probably know it. I hope they do!