Contracts are invalidated all the time.

If they do that and if they get hold of the individual (or their assets) the court can force compliance in the usual ways.

"I can't access it and never will be able to" is not a believable excuse unless you can prove it.

A "smart contract" isn't a contract in any sense of the word, so I'm not sure what you're trying to argue here.

Make sure you do it with a defi flash loan