Tenant subleasing or not

[Marcus Johnson]

I have a duplex in South Minneapolis and unit #1 has two tenants who signed a year lease.  They have always paid on time, but recently a tenant who just move in just over a month ago wrote to me that she would like to sublease the unit and was looking for my approval.   The other tenant wants to stay and found a replacement tenant that would like to take over the moving out tenants spot.   I've started the background check process on the prospectus tenant and am waiting for the rest of the information to come back.  Thus far her salary, landlord history are spotless and qualify.  I am waiitng for the criminal history come back.   

So I understand that in Minnesota that if you sublease a unit, then the subtenant pays the tenant and the tenant pays me.  The question I have is if all parties involved agreed that we sign a written contract voiding the existing contract ending on 10/30/2018 and then have the existing tenant that wants to stay and the new tenant sign a new contract, why wouldn't that work?