One of Two Things to happen with Tony after 24 - Solitary:
24 Solitary is likely just a set up for Day 10, in which Tony will either:
1) Redeem the things he did after Day 5, being secretly recruited by Christopher Henderson, then working for Emerson's crew (doing many 'bad things') leading up to Day 7 and the killing of FBI Special Agent in Charge Larry Moss, taking a shower beside a corpse, and the deaths of other innocents in the name of Michelle and his unborn son. (both would condemn his actions to get to Alan Wilson) The redemption storyline would be the most popular I think, but 24 is 24 and it's unlikely writers would give us a predictable redemption story for Tony.
2) Tony continues down the path of darkness, working for the bad guys, killing innocents, and blaming Jack for all his problems--after all it was Jack's family, most notably Graem Bauer that hired the hitmen that killed off Michelle Dessler and his unborn son, just to get Jack out in the open. No matter what Jack says to Tony, he is wrong and Tony continues to descend into most hated villain on 24. Tony will eventually work with one of the first evils to grace 24's cameras, and one that even threatened his own life a decade earlier, and the one who has escaped Jack's justice: Mandy.