This whole thing is way too painfully
Spinal Tap. Tarja's public handling of it is more dignified than the band's, but that doesn't mean her private behavior wasn't exactly as divisive as they intimate.
Given that I'm never likely to learn the truth, I guess I will have to side with the band on the practical grounds that new Nightwish music with another singer seems more likely to appeal to me than Tarja's solo work.
But just in case neither one pans out, my current runners-up to Nightwish in the same general style are
Darkwell,
Asrai and
Epica.