What happens at the end of Dead Space 2

Isaac destroys the marker, after Tiedemann attempts to kill him, and Nicole attempts to "absorb" him into the marker. Ellie breaks through the marker containment area in the gunship she escaped in, and saves Isaac. The final scene shows Isaac staring crazily at Ellie. after the credits, a conversation is heard that there are atleast 12 marker sites, and that they need to "pick up the pieces".