I don’t think it needs to be balanced as harshly as “sacrifice myself and 1 other to get 1”.
First off, no one troop in GoW is powerful enough to warrant that (unless it comes back with buffs.) Second, we already have similar traits: plenty of troops summon another troop on death, and Infernal King summons itself on death. The Dragon Soul also used to be able to resurrect itself. Sunbird also resurrects.
Now, these aren’t quite the same mechanic. The one you’re talking about resurrects a troop that’s already been dispatched, not the caster. So I kind of understand the want to balance it harshly. But if it’s a 2-for-1, it means there are a lot of situations where you simply can’t cast it. What if you only have the necromancer-type-troop left? There’s no way to cast. What if you only have 2 troops left? It’s probably not worth going down to 1 for any troop in the game.
I think 2-for-1 is too much. “Sacrifice myself to bring back another troop” might be useful. It’s hard to imagine. If you’re winning, this troop’s kind of useless, so I’d want it to have a nice set of traits. If it doesn’t sacrifice itself, I’d kind of like it to be a one-cast-only thing. I think if it had a pretty decent set of support traits and sacrificed itself to get back 1 troop (at base stats), it’d be a very powerful mythic that’d find a team or two it could settle in.
My only objection to the mechanic in general is I don’t think GoW is a better game when it last longer. The more gem matches you make per game, the more likely you will see “extreme luck” on either side per game. Everyone’s happier the less we see those events.