My tenant just informed us that they were terminating a 2-yr lease with 10 months remaining on contract.

NEVER EVER hold real estate long term in an S-corp or C-corp.You will most likely want to hold that rental in a partnership between the two of you.For an accountant do not feel like you need to use someone local.

This usually looks like a little black cylinder, about 1/2"-3/4" diameter and 1/2" high, with a couple of tab terminals sticking out of it, and wires plugged on to the tabs. 

Well we were over there the other day to replace all the batteries in the smoke detectors and noticed that it had been removed...Besides being rough on the apartment, the other tenants have told me that he's yelled at them numerous times, slammed doors right before they could get to him, etc.

This is part of my lease:It is understood and agreed that a single violation [illegal activity] shall be cause for immediate termination of the Lease and eviction from the premises.

Fast forward to today and we are terminating our loan and escrow.

Demand is hereby made that you remedy the noncompliance within 7 days of receipt of this notice or your lease shall be deemed terminated and you shall vacate the premises upon such termination.

The tenant has asked to terminate their lease because of the conditions, stating they are unhealthy for her and her pet.  

The best you can hope for is a tenant that will voluntarily agree to terminate and remove their possessions.  

The only thing a Realtor or anyone can do is terminate a contract if they didn't prefer wholesalers.