This would be a case-by-case basis, but it should be noted that not all breaches of contracts or defaults on loans are equal. With the advent of the DNT, there's been a policy change re defaulting on loans, where yes, you will be banned (as usual). However, the length of the ban will be determined based on the loans outstanding. After a period of time, you may be DNT'd (let back into the community but still banned from the market), on the rationale that you've served your punishment and the debt remains outstanding.
The same would apply for breach of contract. If it wasn't fraudulent (ie a scam), then you would still be permanently banned, and the damages/compensation flowing from the breach would form a debt you'd have to repay, and after a while, once you've served your punishment, you may be DNT'd.
So although you could have it in your contract that IF they default on their obligations, then they would be permanently ban. We would recognize it insofar as the fulfillment of the promise was very important to you, and thus a failure on the other parties part to adhere to it would be taken into consideration. I'd also think the more formal the contract/document, the more we would take it into consideration for the same reasons.
In summing all that up, there's probably no term you can put into a contract to ensure someone is 100% permanently banned forever, never to return. However, we will definitely take the contract into account when determining the length of someone's punishment, and so on that point, we do recognize contracts, but it really depends on the individual case.
Feel free to run any specifics be me, and I'll try my best to help.