by the looks of it, the juggernaut arrives rather fast at the planet, seeing it steps out of some hyperspace-like superspeed when breaking through the clouds. that suggests the travel time probably will be not that long. Then we need to remember david's head is not connected to this body. we see from the holograms shaw knows what she's doing operating the table so we can assume she's capable of piloting the ship somehow, so it's not david who flies the plane.
Somebody reattaches david's head, he can't do it himself obviously. We also see david unleashes the payload on the planet, so he has been 'fixed' meanwhile and somehow is motivated to bomb the planet. i assume the payload will be dropped upon the buildings, and the crowd will flee into the centre circle and then somehow get burnt like a crisp. shaw taking off in a ship that will cause it's engines to kill the citizens? just inventing stuff here.
You can't convine me that the black goo all of a sudden becomes a sort of napalm substance, so i don't think the black goo will murder the citizens.
Another weapon that David fires off however, is another thing to ponder about though. I remember some mentions of lightning.
but getting back to the op.......nowhere is it stated they are stranded or marooned. there's a difference in being on a planet for a reason and not being able to leave. LV-223 had a bunch of ships parked, they could leave easily. There is no reason to assume there wouldn't be something similar to the paradise planet especially seeing there's another differently configured ship in the tv spots, so little chance they could not leave in any way.
Im also sure that the information will be there how they invented this form of travel (magnetism somehow) and david can read the stuff so he'll find out in a whim and then you're almost there already.
again, the question is, A) will shaw actually be still on the planet and alive? and B) who says then shaw is still on the planet and not already left, not knowing there's a facehugger aboard and she will crash into lv-426 at some point, and C) how on earth did people reason that they are stranded?
because shaw send a distress call? well, it remains to see if it's actually that. a message is something different than a distress call. she also sent a message whilst on lv-223. she's not there anymore for 10 years.