Rahdo said the syringe from the demo was the Medics default revive.
"Join reinforcements" will probably just make you un-revivable, and you will spawn in the next wave. In the meantime, you can goto the limbo menu and change your class and loadout for you next spawn. Also, the limbo menu was accessible at anytime in previous games, so you could choose what you want to spawn as the next time you die. With the inclusion of Command Posts in Brink (able to change class/loadout on the fly) I don't know if they will include it. I think they will still.
