Business Rule assigning to technician no longer in service desk plus

Business Rule assigning to technician no longer in service desk plus

We have a business rule set up that was set to assign to a specific technician. That technician left and was removed from service desk plus. However, the business rule still exists. Any time this ticket is created it assigns to the same technician but there is no other rule telling it to assign to that person. 

It still runs the rule. How does it decide who it should assign it to when the other technician is not here anymore? 

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