LT League vs Heroesworld.ru

I didn't find any rules in the SOD that prohibit upgrading vampires. If that's the case, then there's a reason to switch to a secondary Necropolis if you have one available.

Also, based on the template structure, two zones will always drop either a Conflux or a Necropolis. If you add to that the fact that a Necropolis can also drop in the remaining 6 zones, then you can conclude that Necropolises will always be available on Balance with a 95% probability.