I think a lot of times fish kept in poor conditions such as is usually the case at Walmart die because they come stressed and/or diseased and the average/beginning aquarist does not know how to minimize stress and treat them (i.e. I'm pretty sure most average aquarists do not have a cycled quarantine tank set up and going for new arrivals). Of course, there is still always a chance of a weakened fish not making it despite the best efforts being made, but bettas in particular are quite amazing little survivors and I'd say he has a good chance with Kara .

It does look like another betta was in his cup. If it were merely fin rot, there would probably be blackened/shriveled ends on his torn fins. However, with his fins being torn, he has a much bigger chance of getting fin rot so Kara is doing the right thing by treating him as a preventative measure. She's probably doing very regular water changes and using something like StressCoat as well as adding aquarium salt to help heal the wounds.

At one time I may have been more skeptical of his chances too, but I have witnessed some amazing transformations (especially by BettaMomma on TFF and her 15 rescues ).

Good luck with the little guy Kara, and bless your heart for rescuing him. I'm sure no one else would have wanted a betta with torn up fins and he'd have died there. You'll have to post pictures as he grows back his fins