Eddie Sefko of the Dallas Morning News reports (via blog):

Tim Thomas will not return to Mavericks

Tim Thomas has decided not to return to the Mavericks because of the situation with his ailing wife.

Her condition, which Thomas and his family prefers to keep private, forced the 6-10 forward to stay with her much of last season.

He played with the Mavericks for the first half of the season, averaging 7.5 points and 2.3 rebounds in 18 games. But he left the team in January - with the Mavericks’ blessing - to care for his wife.