A different line to consider here is to call them and tell them the situation that there wasn't an attendant and see if they'd wave the fine. I've done it before and it did work once for me.

As for the original question, there is a case that they could file a claim against the owner of that vehicle and report what was done, in this case trespassing comes to mind as an initial compliant that one could file. Alternatively, they may claim that by parking on their lot you agreed to terms and they want to enforce those terms.

While it may seem like an empty threat, you never know how karma will come back and allegedly it can be pretty ugly in some cases.

Was there a way to pay even without the attendant? If there was, then you probably should have paid, and like JB King replied, they can claim tresspassing or some such. If there was a clear statement that it was paid parking, and there was a way to pay, with or without an attendant, you are obligated to pay, if you choose to park there.

They most likely cannot do anything. Likely if you read the ticket it will say the penalty for not paying is that they will tow your car, but as you are already gone that does not matter. They put your license plate down to make it look official, but they do not have access to your info from that. Anything thing else they would not be able to prove that it was you that parked your car there (could have been a friend or something). So through the ticket away, I just would not park there again without paying as then they might tow your car.