I think he'll be convicted, but won't get six years.
You're right, his career is over. He may have not killed those dogs, but those dogs were his, and the house was his.
Even though the cruelty to animals is irrelevant in this case, (not what he's being charged for) the prosecutors will bring that up, which is going to absolutely kill Vick.
There's enough circumstantial evidence to get him.