Are you telling me that the worst version of the Black Death was 3-4 orders of magnitude more deadly than previous strains? Because that’s what would have to happen to this coronavirus for the scenario you are talking about. If this is even remotely possible, then I assume we should also be worried about the influenza virus, or really any other common household pathogen, because who knows what it could mutate into.

Or maybe you should keep your doomsday theories to yourself.

Even with modern medical care the worst version of influenza had approximately 60% fatality rate (H5N1). https://en.wikipedia.org/wiki/Influenza_A_virus_subtype_H5N1

COVID is already significantly more dangerous than normal Influenza so making that kind of jump is far from impossible