I'd go after Miguel Cabrera, at least as one of a number of options. Even if his defense tanks like some seem to think it will (I see no reason to believe it must), he's an elite bat and has demonstrated in the past that he can tolerate a move into the outfield.
He's about on par with Jason Bay in left field, if you're willing to pay Bay you should be willing to pay for the same or better production in a body 5 years younger.
That said, the Tigers really haven't showed any signals that they're really thinking of packing it in at the moment and haven't really thrown out any obvious signals that they're considering blowing it up. They'd like to shed salary I'm sure, but shedding it by getting rid of their best player isn't probably what they have in mind.