You will soon get an upgrade icon on Win 7 or Win 8 machines. That will put there as part of your normal updates.
This will be a free upgrade to Win 10.
You will probably not need to restore to Win 8 but you will have an option to do so. I am using Win 10 now and it is working fine.
Yes Win 7 will stop being supported at some point. I don't think Microsoft has announced the exact date.