Destroyed-or-departed-delay

destroyed-or-departed-delay
        Returns true N seconds after all the listed ships or wings have been destroyed or have departed.

Takes 2 or more arguments:
        1:      Delay in seconds after the last ship/wing is destroyed or departed this expression can return true.
        2+:     Name of a ship or wing

Notes

You can use the following SEXP tree to emulate a nonexistent check-if-ship-is-present SEXP:

- op and
   - op has-arrived-delay
        # Ship
        # 0
   - op not
      - op destroyed-or-departed-delay
           # Ship
           # 0

where has-arrived-delay is needed if the given ship isn't present at mission start.