While I cannot comment on the OP's specific situation, I have learned my lesson on this one. There were a couple times where, for whatever reason, the folio wasn't slipped under the door. No big deal. The folio was always emailed a couple days later.

But then....

I got a folio via email where I was charged for a second night. The hotel thought I was still there. While they were good about reversing the charge for the second night, it was really my fault. Now, if I don't have a folio slipped under the door, I stop at the front desk to make sure they dont think I'm staying an additional night.

With that stated, I slip the folios in my bag and put them in a drawer when I get home, never to look at them again. Every couple months or so, I throw away the old ones. Having them available online is awesome, and sometimes I charge something to the room in the morning which would not be on the one slipped under the door.