Steps to reproduce:

1. Configure trigger action with one or multiple host groups as conditions
2. Delete host group (which is part of the conditions)

Result:
Trigger action gets disabled
Expected:
Trigger action remains enabled if or while attempting to delete the host group receive a message indicating the host group is still in use.

If there is no other condition in the action then it is logical that it is disabled. But if there are other conditions the action should remain enabled.