What's a symptom of a hard fought game?  Lots of deaths.

What happens when a demigod dies? Downtime.

What does a losing team need more than a winning team?  Shopping, skill upgrades, skill selection and inventory management.

What do generals need more than assassins?  The same.

When are those things easiest to do?  Downtime.

Let players queue their choices while they're dead and have them snap into effect when they're reborn.

You can put whatever restrictions on it you want, make only skills or only summoned minions or only citadel team upgrades or whatever, but the net effect of death buying will be a slightly faster game, a better more generally experience for generals, and a balancing boost for losing teams that doesn't extend the game needlessly, cause everything gets deadlier.

It also makes death a little more fun, since you're out of the action but not out of the game staring at a gray screen.