It's not going to live more than 2-3 days in a 1g container with no filtration or heating. Also, even if they do purchase a larger tank, a person that is so unknowledgeable in the hobby that they put an Oscar in a 1g container w/ no filtration or heating isn't going to properly cycle the tank.
I'd say he's a goner any way you look at it unless OP could possibly get ownership of the fish and then just bring it to a LFS with a cycled tank that's at least larger than a 1g container. Of course then chances of another person purchasing him from the LFS and doing the same thing to the poor guy are very likely, and then he's out of the frying pan into the fire.
Sadly, we see O treated like this in the hobby on a daily basis. They're a very common target of abuse from unknowledgeable fishkeepers.