If he has it again, he'll almost certainly be asymptomatic and will get over it quickly.

I've previously said people can't get the same kind of coronavirus twice. I now know that to be incorrect. It was based on what I knew about how the body reacts to the Common Cold, which is also a kind of coronavirus... but I subsequently found out that only about a third of the hundred or so CC strains are caused by coronaviruses. The rest are caused by rhinoviruses. You can never get the same rhinovirus twice, but you can get the same coronavirus twice. However the second time, the body is much better equipped to deal with it, and mounts a strong secondary response.