Neither. Those should not be the two options that face this fish.
Buying and combining fish like this with either no research ahead of time that would have warned you of this potential outcome...or knowing about it and willfully ignoring it...and at the same time not having adequate alternate housing...is the problem. And calling your 400-gallon tank a "pond" is just playing word games. If you have a one-acre body of water you can call it a "lake" if you wish...but it's a pond, plain and simple. In terms of natural bodies of water, 400 gallons isn't a pond; it's a puddle.
Harsh? Maybe. But...how long did the Jag hammer on the Oscar? He didn't kill it in seconds, it took some time, and a bunch of repeated and brutal attacks. Did you just sit and watch that? That's harsh.
I'm sitting next to a 30-gallon tank as I type this, and I'm imagining somebody trying to shoehorn a 10-inch Oscar into it. Animal abuse like that is harsh.
Don't you have another thread going with questions about what fish to buy for your hoped-for big pond next year? Perhaps you should be concerned about the fish that you are currently abusing and killing rather than the ones you plan on adding in the future.
And trying to blame this mess on somebody else, i.e. your father, is really the icing on this cake.