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:

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

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