The BBC profile says he had been sidelined for a year:
He was reportedly under a form of home arrest since May 2011, following his meeting with the opposition to try to start a political dialogue and also because of his opposition to the clampdown.
Assad’s toast. Defections signal the end just like with Saddam’s regime and Ghaddafi’s regime. No doubt Assad will be smart enough to use a poison pill or a bullet rather than wait to be executed.
If Tlass is anything like his father, Mustafa, Assad is probably better off without him. Mustafa apparently went out of his way to propagate anti-Semitic fictions, and was prone to making borderline insane statements:
In 1998, Syrian Defense Minister Mustafa Tlass boasted to al Bayan newspaper that he was the one who gave the green light to “the resistance” in Lebanon to attack and kill US marines and French soldiers, but that he prevented attacks on the Italian soldiers of the multi-national force “because he was in love with the Italian actress Gina Lollobrigida.”  Mustafa Tlass had also allegedly boasted to the National Assembly about atrocities committed against Israelis who fell captive in the Yom Kippur war. “I gave the Medal of the Republic’s Hero, to a soldier from Aleppo, who killed 28 Jewish soldiers. He did not use the military weapon to kill them but utilized the ax to decapitate them. He then devoured the neck of one of them and ate it in front of the people. I am proud of his courage and bravery, for he actually killed by himself 28 Jews by count and cash.” 
There are three missing Israeli soldiers in the Bekaa valley since the June 1982 war in Lebanon. Tlass allegedly told a Saudi magazine: “We sent Israel the bones of dogs, and Israel may protest as much as it likes.” 
During his career, Tlass also became known for colorful language. In 1991, when Syria was participating on the Coalition side in the Gulf War, Tlass stated that he felt “an overwhelming joy” when Saddam Hussein sent SCUD-missiles towards Israel. In 1999, Tlass caused a minor uproar in Arab political circles, when he denounced Palestinian leader Yassir Arafat as “the son of sixty thousand dogs and sixty thousand whores”. Earlier, in 1986, he had called Arafat an “idiot” and a “puppet of the Americans”. The long-standing conflict between the Assad regime and the Palestine Liberation Organization would not end until after Hafez Assad’s death in 2000.
In an interview which aired Russia Today TV on June 8, 2009 (as translated by MEMRI), Tlass claimed that Actress Gina Lollobrigida had once told him that he was the “one love in my life.” He also claimed that Lady Diana wrote him letters that “were full of love and appreciation.” He also claimed that Prince Charles has given him a submachine gun as a gift.