when an item is disabled, all triggers referencing it should be set to unknown and their error field populated with an explanatory message.
when a host is disabled, all triggers referencing their items should be set to unknown and their error field populated with an explanatory message.

suggested messages - "One or more items that are referenced in this trigger have been disabled or belong to hosts that have been disabled".
message is not translatable at this time (see ZBXNEXT-567)

if the trigger is not already in the unknown state, unknown event is generated for it (to be discussed still)

for 2.0 a db patch should be developed that sets such error message properly