This topic has been discussed multiple times already. Please use the search function or google and read up on the subject.
There are no known ways that quantum computers will break sha256.
Exactly. Also remember that in the event of a super power quantum computer trying to break the sha256 hash they will need however to compete with the majority of miners together which secure the network by definition. It would be a fail cause I think that noone can override the power of a peer to peer network of such capabilities as the one of Bitcoin in the future when this kind of attack could happen.