Congratulations on your new used pop-up. As for the cable, you did not do anything wrong. The cable was probably already compromised and only holding on by a thread, and would have failed no matter who had cranked it up, ether on that trip or on your next trip. We had a 197X Starcraft pop-up, at some point I think every cable was replaced at least once.
My brother had the same critter issue a few years ago with his pop-up, with very similar damage. I am not sure though what they did to sanitize the tent walls, but I do know everything was opened up and cleaned thoroughly. The worst part I was told was the cushions as they opened them up washed the covers and then washed the foam, it took a few weeks for the foam to dry (ick).
There are lots of things people swear by to keep critter out, this is what I do to any trailer, and we have never had a mouse issue. I get on my back and crawl under the trailer and look for every single hole, and fill it. You will be surprised how many there are. I use a combination of steel wool (I really like the brass scrubby pads) in the hole first and then a little marine sealant (caulk). Then after every trip, as we are packing up we wipe everything down good. At the end of the camping season, we remove all critter food potentials, then we scrub and bleach all the areas food may have been. Then I place a few bait blocks around the inside (mice just cannot resist them) to indicate if there were any critters in the trailer (if they are chewed on, critters have been there). I also add a few sticky traps, but they only work if the critter walks on it.