Sending doesn't have a range limit, and explicitly works across planes 95% of the time.

The big question here is what mechanically is them. Spells like Revivify target a dead creature, which means if the corpse isn't the creature the spell won't work. But there's also no rule that dead creatures can't talk or take actions or whatever, so you'd still be able to use Sending or just ask them normally. But that's assuming they are a creature. The section on improvised weapons says that a dead goblin is an Object. If dying turns a Creature into an Object, then it could no longer take actions. But there's also nothing saying that Creature and Object are mutually exclusive. maybe a corpse is both?