Tenant seems to have vanished

Hello

I have a HMO property which I rent to individual tenants per room. One of the girls seems to have just left and gone back home abroad. Her monthly rent was due on 1st October. Her clothes and such are gone except for a few ornaments(lamp etc). She also left the keys in the door. Can I look for another tenant straight away or is there due process even in these situations to avoid a comeback from the tenant (claiming they went on holiday or something).

Kind Regards
Raj