If you kill Gale and don't resurrect him for 2 days, he wipes out your whole party and you have to reload a save, so it seems it's a ticking time bomb that you can't leave dead.
You should be able to pick up a Revivify scroll if you don't have any other options. There's at least 3 accessible in Act I. You may need to use stealth to get to them if you're level 1 or 2 though.