I believe that if the Hawks Organization pay him the 100% signing bonus, then what happens after year 3 or year 4 when he doesn't make as much money?
Would be another holdout....
Please take a moment to understand what the issue actually is here. It's not what you evidently think it is. The amount of compensation is not the issue. The cash flow in later years of the contract will be lower than in the first year, and that's not negotiable. Neither is the amount of the contract, nor how much of it is signing bonus. Those things are all already decided.
Witherspoon will be given a four-year contract worth a fully guaranteed $31.86M of total compensation, $21.17M of which is the signing bonus.
The only issue is a cash-flow issue. Witherspoon wants to receive 100% of his signing bonus immediately, like the three quarterbacks drafted ahead of him (as the first, second, and fourth players in the draft) did. The team wants to defer payment of part of the signing bonus until later. The Texans paid the other player drafted ahead of Witherspoon, Will Anderson (third pick overall in the draft), 85% of his signing bonus initially, with payment of the remaining 15% scheduled for later.
So first of all, once the contract is signed, the Seahawks will have taken on a legal obligation to pay Witherspoon 100% of his signing bonus, and in fact, 100% of the whole $31.86M of total compensation for the contract, over the four years of the contract. Neither side, nor even both sides together, can change the amount Witherspoon will get from this contract, nor how much of it will be a signing bonus. The only issue is how many actual bank transfers will be made to pay the $21.17M signing bonus. Witherspoon wants more of the bonus paid immediately than the Seahawks want to pay immediately.
Second, there is no chance for "another holdout" later. Right now, he has no contract. In the third or fourth year of his contract, he'll be under contract and therefore unable to hold out.