I don't suppose Garp would be enough of a ransom to get Teach his kingdom, would it?
I can't think the WG cares that much about Garp, but it's more feasible then Koby.
Garp is getting Dishonorably Discharged.
IMO, Imu's allowed Garp to exist so long, because Garp was great public morale for the Marines. Same way Imu was fine with luring Harald in so he wouldn't go against the WG.
Cipher Pol is good at their jobs: if they found out Ace is Roger's kid, am I supposed to believe they never found out Garp's ties to Ace/Rouge?
How do the Marines act if it's revealed Garp:
1. Covered up Roger's child and helped raise him, leading to the pregnant woman hunt and Marineford
2. Freed Dragon, because he was his son, who became the "world's worst criminal"
3. Refused to capture Luffy in Enies Lobby, because Luffy was his grandson, leading to Luffy in Impel Down/Marineford
The WG has LEGIT GROUNDS to dishonorably discharge Garp for all his insubordination. If they have info Koby was on Alvida's crew, they can cut ties with Koby, too. Possible Dadan gets arrested, as well.
This, along with Vegapunk's announcement, will lead to a huge schism in the Marines, IMO.
We'll get a Sword-focused splinter faction rescuing Garp from Cross Guild's public execution of Garp (Ace parallel).
IMO, the Garp rescue arc is where Bogard will get his time to shine.