That is the point. If you know you are going to break the contract you shouldn’t sign it in the first place. And as I said, even if it’s not illegal it’s not morally right.
And if you do break the contract you should leave the contract and stop using whatever service you have been using in case UE4. But even when they break the contract with Epic they don’t stop using Epic’s engine and instead want to find a way to prove they have the right to break the contract and still use the engine. That’s again a moral.