Let me tell you all a story:
About a year ago my brother decided to cat-sit his ex-gf's two cats in me dad's basement. We'll refer to them as the "boarder cats"
There is already a resident cat about 10 years old who is quite cranky and generally does not like anyone else although she can be nice when she wants to. We'll refer to her as Queen Bee.
The two boarder cats were locked in the basement for around two weeks so that queen bee couldn't get at them but she knew they were there.
Anyways, the boarder cats ended up leaving after maybe two or three weeks. The day after they left Queen Bee has been shitting and pissing down in the basement much to our chagrin. This has been going on for almost a year, on and off.
Queen Bee has ruined all the furniture down there (the basement was fully finished). We just had to throw all that furniture away, probably cost around $4,000 new.
Now the basement is totally empty with exception of a telly and queen bee has started using her proper litter box again on the first floor.