What are the liabilities for licensing/subletting after it has ended?

I let an acquaintance use my apartment for a fee, to help him out with his living situation. I retained some access to some small parts of the premises. There is a no subletting clause in my lease, which says: "Resident’s right to possession shall not be assigned nor the Premises sublet." The written agreement between me and my acquaintance is styled as a license agreement rather than a sublease. He broke the agreement, so we agreed to a thirty day notice, at which point he promised to pay a prorated amount for 8 extra days at the end. That acquaintance moved out 7 days early (he acknowledged staying one day in) and refuses to pay for the rest of the license fee (or rent) of 8 days. I am thinking of going after him for the nonpayment, but am concerned about what my landlord might do if they find out about the license agreement (for example, if the acquaintance retaliates, or if the landlord peruses small claims cases). The acquaintance has vacated and no longer has access, so all that is in the past, and nobody else is in the apartment. What are the legal risks if the landlord finds out at this point? Assuming that the 30-day notice and accord was valid between us, can I get the 8 days that he skipped out on, in view of the no-subletting clause in the master lease?