The blonde survivor that Alissa asks whether or not she has a boyfriend is Nicole, Isaac Clarke's girlfriend from the "Dead Space" videogame, which takes place after "Downfall".
The movie ends right where the video game begins.
The movie is a mix of classic hand drawn and cg animation. For example, the USG Ishimura and the transport shuttle are both computer generated.
The Necromorphs are a lot smarter than first believed. The entire reception room of the docking area was full of Slashers just moments before Isaac and his crew announced their arrival, for the game to start. Explaining the surprise attack in the game.
Even if the shuttle was successfully destroyed, preventing an infector from boarding, the Marker would have eventually created one on-board.