Business rule for Logged in accounts

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Hi, 

I have a request to create a business rule that will assign status = customer reply incidents only to an account that is logged in (according to specific queues). 

So say an agent answered a new incident, but when the customer replied the agent was logged off- I would like the ticket to be assigned to null, and not to the agent who previously responded to the customer. 

Can this be done in the business rules? 

Thanks, 

Shaina