My only (known) experience with coronavirus is in the feline infectious form. For the most part, it is an annoying but harmless but that tends to give cats the runs. Unless finds an immunocompromised host, such as one that had a previously undiagnosed case of FIV. In that case, it doesn't get fought off effectively by the immune system, it just sticks around in the lower GI tract doing what viruses do: making bad copies of itself. Eventually one of those bad copies happens to be a version that can cross the epithelial lining in the peritoneum. Once the peritonitis starts, there is no way to stop it. It is currently always fatal. After two weeks of feeding him via a feeding tube and watching this once lively and happy creature struggling to find any way to lay down that didn't hurt... putting him down was one of the hardest things I've ever done.
George was only 4 or 5 years old. We'd only had him for 2 of those years. We were looking for a hard-luck case from the local animal shelter, an older cat since those so seldom get adopted. He was a sweet, very very affectionate boy. He must have had the FIV that made him vulnerable when we adopted him, and some how he gave a false negative when he was tested.
As far as I know, human coronavirus has no such tendencies to mutate into something lethal that can cross into the peritoneum. I've done a superficial search of the online literature, and I haven't found anything yet. Feline coronavirus and human corona virus are not the same thing, they just have a lot in common. For the most part, I expect it is just going to give people upset bowels until their immune systems fight it off.