It takes a little practice, but it won't take you long to be able to start your bike from rest on a steep uphill. (There is one short climb outside my office which I measured at 12 percent grade. When I first bought a recumbent, I would stall on that section even if I was already moving. Within a few weeks, though, I could start from rest on it with no trouble, as long as I'm geared way down.)
Worst-case scenario, though...if there's a stop sign, there must be a cross street. If you really can't get the bike started again -- forgot to gear down far enough before stopping, maybe -- you could always turn right onto the (hopefully less steep) cross street, pull a U-turn, and turn right again.