The point you are missing is that this is how EVERY virus and pandemic has progressed throughout eternity. with or without vaccines.
Yes, new variants will arise -- which has NOTHING to do with "humans mutating the virus" -- just due to normal RNA transcription errors plus the occasional recombination with other viruses and variants. The point is that any new variant that is either less communicable than Omicron and/or more lethal, will generally not take hold because it will not be able to compete and exposure to Omicron will give enough natural immunity to protect from later variants. So, if a new variant does arise, then it likely will be, if anything, LESS pathogenic than Omicron, not more. Killing your host or making them too sick to go out and spread the virus is the WORST thing for a virus to do, evolutionarily speaking. It is very rare, almost unheard of actually, for a virus that is endemic in the population to randomly develop new strains that are more deadly. Typically, just the opposite happens. The viruses that cause pandemics generally occur when a virus initially makes the leap from a different species to humans, who have no natural immunity to it. It is then a tug of war for a couple of years as the virus adapts to the host and our immune system adapts to the virus. At the end of this battle, one of three things typically happens: the virus mutates to a strain that has so many errors that it basically breaks down and dies out (which may be what has actually happened with Delta in Japan), the virus mutates into something so mild that it becomes endemic to the population (i.e. yet another common cold virus), or the virus in very rare cases adapts so well to the host that it can live in them almost forever without causing serious illness except when the immune system weakens (e.g. varicella -- chicken pox/shingles). From everything I am seeing, one of the first two cases is what will likely happen with COVID19. SARS-1 likely went the first route, which is why it essentially disappeared completely. COVID19, at least in the case of Omicron, looks like it may have had a "fortuitous" (for both us and it) case of recombination where it swapped a sequence of 9 RNA codons with a cold virus in one of its hosts -- which essentially made it more like a cold, in ways that were good for both us AND the virus. Welcome to evolution.