Liquipedia has a nice summary about the last month:
On August 21st, Stephano was reported to have declined Millenium's offer and that he wouldn't be re-signing, which meant that he would become a free agent on September 1st, at the end of his current contract. Stephano's last apparition under Millenium's colors took place in the 2012 MLG Summer Championship, three days after the announcement of his planned departure from the team. Being seeded in group play thanks to his performance in the Summer Arena, Stephano was quickly sent by viOLet into the lower part of the bracket. He nonetheless made it to the group finals, at the expense of Rain, Heart and TheStC, only to be defeated again by viOLet. Stephano met Revival for his first match in the championship bracket, and was soundly beaten by the Korean player, hence being eliminated of the tournament. A the end of the month, Stephano was invited to replace ThorZaIN, who was ill, in the online tournament MSI Pro Cup #13. He eventually won the event, realising his last achievement for Millenium in their own cup, the day before his contract ended
Source: EG Falling