here are the pertinent facts that i do know:
-If a player truly retires, his contract disappears and his contract neither counts against the cap nor can the player be traded
-Only players actually on the roster can be traded
-if a player is cut or bought out, either the full contract amount (if cut/waived) or the negotiated amount (if bought out) still counts against the team's cap, but because of the above bullet point, said player/player's contract cannot be traded.
Therefore, Sheed/Sheed's contract is not a tradeable asset even if it does still exist, and if shaq retires, the same goes for his contract.