Hi,
Apologies for the pretty late answer on this thread. Though it is not possible to change this behaviour, you can still create a new ticket out of the response sent to an older ticket using multiple automation rules.
Rule 1 -To identify deleted tickets :
Create an observer rule with the following specifications :
Events are performed by -> Agent
And the event is -> Ticket is deleted
Actions : Add tag -> Deleted tag
Rule 2- To split the response sent to the deleted ticket :
Events are performed by -> Requester
And the event is -> Reply is sent
Properties -> Tag is Deleted ticket
Actions : Trigger webhook ( use FD API) to create a new ticket
Cheers!