The Mavs are over the cap so they have no ability to give Nene the type of contract he would be looking for.
They will prob. just amnesty Haywood.. problem solved
The Mavs are so far over the cap that amnestying Haywood would not get them under the cap.
It would also be ridiculous to jettison Haywood when he has value as a trade asset, especially considering he has a fully unguaranteed final year on his contract.