Let's skip omicron for now.
While the original strain was evolving in patient zero it was acquirng various random mutations.
The ones that were not beneficial for infecting human cells and thriving in humans didn't survive.
Threre were few possibilities.
I don't think it could evolve some mutation that would trigger immune system of that person into overdrive causing it to kill all variants of the virus. Very unlikely.
Other option is that this virus might have evolve lethal mutation and kill patient zero without infecting anone else.
And the third option is that eventually virus did stumble upon mutation that increased viral load that this person was shedding to levels sufficient to infect another person.
And since it managed to break out of a person that was fighting with it for months or years it's no surprise that it did well in the next and next billion that followed.
The above is most likely scenario for me.
I think we'll eventually find closest relatives of that virus in some civet somewhere. But that will prove exactly nothing to anybody who believes in lab leak origin.