I tested this out in a couple of games. On purpose I didn't let the couples try for babies. In one game I even turned away an orphan who showed up on the doorstep; I felt really hard-hearted then.

In both cases the survivor received and accepted proposals for a second marriage. However, since the new spouses were about the same age, the marriages only lasted a short time before they both died. Because there were no children to carry the game into the next generation, the game was over at that point.