There was a piece on the WSJ last week, that the negotiation of TAM joining the Oneworld that was supposed to take all the way until March, 2013, is almost wrapped up according to the unnamed sources cited by the paper.
When the AviancaTaca joined the Star Alliance earlier this year and when the merge of LAN and Tam was approved, it was made clear that TAM couldn’t stay in the same alliance as AviancaTaca. The only two remaining options are SkyTeam and Oneworld. Delta bought a share of TAM’s domestic rival GOL, so it is unlikely that the alliance choice would be anything else than the Oneworld.
It seems rather likely that TAM will cease to be a member of Star Alliance sometime in the early second half of 2013. Obviously, all the award tickets will be honored past the exit date, but you won’t receive miles or get Star Alliance related status benefits once the airline has exited the alliance.