The fundamental problem here is if the story is true, Elin doesn't trust Tiger.
I get that Tiger cheated and that she was publicly humiliated by the stories of his indiscretions but that was the past and she was compensated quite well for his poor judgment.
If they are going to reconcile she can't put a bounty on the relationship failing. If the only way she will agree to marry Tiger again is if he puts up $350M to ensure he doesn't cheat then I'd walk away because that indicates a complete lack of trust. Elin will be reviewing everything tiger does with a fine tooth comb to ensure he doesn't violate the clause.
Can you imagine the negotiations into such an a agreement as to what constitutes a violation of the agreement? This is not how two people reconcile in my opinion if they are still in love and want to be together. As others have said this isn't a marriage it's a business arrangement.