Drones live 40 to 50 days if they aren't ate by a bird or otherwise killed. If they mate with a young queen they die immediately afterwards because their sexual organ is left in the queen after mating.
They do not have any duties in the hive at all. They do not have a stinger so do not do guard duty. They don't help take care of the brood, build comb or help with honey storage. They won't even feed themselves if they can get a nurse bee to feed them instead.
Here's a picture of a drone DH brought to show me back in the spring.
