well, yes any story that kills off the "hero" is mighty brave, audience likes "happy endings" (some would say "crappy" *eg*)

maybe "Prometheus" might have benefited from it - maybe too, if the "Vickers-question" was answered - not left open ala Deckard (even when Ridley remained adamant, that he was/is a replikant)

As for continuation: I strongly believe that both Elizabeth and David are coming back (at least if both actors are available) - is it good or wise?

A nice twist could be to send another team after THEM, and not to ivestigate the "tombs" - though Weyland or Yutani (or whoever got the say) might send more guys into this system, just to knock things up, and see what creepy crawlies turn out (hm, kind of story from "Alien" ?!)

Better not show Liz&David's journey firsthand, just through "found documents" has a bit of "Blair Witch" to it ;-)