I know it has been confirmed that he is in ill health, but has an official source mentioned the 3-6 months to live prognosis?
If Elder Packer is in fact out of the Queue, that puts Perry next. If Packer was removed because President Monson is on his last legs, then that would put Perry next in line. Followed by Elder Nelson, who is also over 90.
I'm thinking there could be a very quick turnover in the next year or so, then Elder Oaks becomes a long term President. I know many here were hoping for a "President Packer" because of the harm he could potentially do, but a President Oaks, with his full faculties, could be just as embarrassing for the Church.