Branded Nameservers

[Matt]

If I request branded nameservers will the sites that are currently going to the gh one's still be viewable until I change the dns settings for the domains?

Yes

I have some sites which I do not have access to their dns - can I leave those as generic even if I resell the hosting?

Yes you can use generic indefinitely. It is managed DNS so it will not be removed.

Thanks in advance!

No worries