Non-biologist here so apologies if the question is violating too many of the community standards for asking a question in the forum.
What got me thinking was imagining how much more terrifying the current situation would have been if the COVID virus had very long incubation period of something like 6 months and a higher mortality rate with the same rate of spread. By the time someone realizes that a virus is spreading, it would have already infected the entire planet. If it has a very high mortality rate as well, wouldn't that pretty much mean the end of the world?
My question is, what is the probability that this can happen? For example, what is the probability that a virus starts spreading with an incubation period and mortality rate of HIV but has the spread rate of COVID?