What happens after 12 weeks?

[suriv]

I have a few family members in the at risk category so are self isolating for 12 weeks. My dad is disabled, has arthritis and no garden so is in his flat for 12 weeks with food being dropped off on his doorstep. The common cold makes him very ill.

But what happens after 12 weeks? Will he go back to normal? Will the virus have disappeared by then? Or will it be extended?

The virus isn't going to disappear. It'll still be there once lockdown ends, and people will still catch it. The purpose of the lockdown is to reduce the peak of cases and therefore reduce the pressure on the NHS. Until a vaccine is found, it'll still be around and most of us will probably get it.