Arguably, the grav drive and the artificial gravity in the ships are two separate subsytems. You power the grav drive, that's just charging it to jump. The artifical gravity seems to persist for as long as the power plant isn't completely destroyed.
Mild spoilers. There's a few levels where it's zero g. Some random encounters where you raid a enemy ship, it's zero g and when you reach the captain's chair, you turn the gravity back on and all the doohickeys like pencils and mugs fall down in a really satisfying way.