once
A hornet can sting multiple times and not die. This is due to the fact that their stinger is not barbed like worker bees are. The exact number of stings is unknown.
Oh, yes! And it's not a nice experience.
No, only Bees die after because wasps and hornets dont leave there sting behind. Bee stings are acidic and wasp stings are alkaline.
Only if you are allergic to the sting, and do not get prompt medical attention.