[Feature Request] Catenation executes a custom function when it stops

[RisingInIris2017]

I need catenation to do such a thing: when it stops, it executes a custom function.
And I can retrieve the reason why this cantenation stops, STOP_WHEN, MANUALLY, UNEXPECTED for example.
Then I will be able to let catenation do something according to its "stop reason".

If catenation is forced to stop (players exit the save they were playing just now normally, or server executes /stop command),
it should return UNEXPECTED its "stop reason", and perform the function mentioned above, then let game/server continues to stop.

It is unnecessary for my request to consider about crashes or something like these.