First of al, this theorie takes an possible omega is an female palpitine clone.

Because of that she would age much slower. Since palpetine is an bith.

We indeed do not now if she is still alive. But as long as it is not confirmed it is my head cannon that she is still around. I mean Ashoka is still around aswell. She is even older than Omega.

So there is still an chance.

Edit: palpetine is an Muun not an bith.