According to realgm -
http://realgm.com/src_freeagents.php?year=2004 - Okur is a URFA and can go where ever he pleases.
He would make more with Detroit, but I doubt they re-sign both Wallace and Okur, when they have Darko waiting for playing time.
I would think the Pistons would keep Wallace and then sign and trade Okur for some one.