You want to structure it like this:
Trigger: Presence sensor 1 or Presence sensor 2 CHANGE
Action:
If both sensors are gone do x
Else if sensor 1 is present XOR sensor 2 is present. then
Do Y
End-If
That will do X if both sensors are gone and do y if one of them is home. The XOR works for Rule #1 because one of you will always arrive before the other and the xor will only be true if either sensor 1 or sensor 2 is present but not when both are. So, when one arrives, the rule fires, when the second arrives, it doesn't.