If the WG doesn't have a secret weapon or some fail proof plan… and if they seriously don't know that Ace is Dragon's son.. then they're total artards.
I honestly think.. they gathered all their forces to meet WB and his crew.. not because they're expecting Dragon to show up. This is how strong WB is... hard to imagine I know.. but YES.. it takes 3 Admirals + All VAs + 7 Schichibukai + every god damn marine on the grandline and their dog to have a fighting chance against WB and his men.
If Dragon or Shanks or anyone else shows up.. then they're good as dead. Even a single person like Raleigh might turn the tide.
How do I infer all this? Just look at the way Sengoku is right now.. even with all the forces gathered at Marineford.. he looks nervous as hell... he looks like a man scared that it won't be enough... he's nervous.. angry.. frustrated.. all at the same time. He's trying to gather every single last person that he can. If WB was really not a match against everything gathered.. Sengoku would look relatively relaxed.. if not downright confident. Sengoku knows how powerful WB is... so I'm sure it's accurate measure of the man's strength.
No Secret Weapon/Plan = WG is totally fucked
The coming chapters will be totally epic because now we have Megellan + Shiyruu + Demonguards/Sandy + 5 VAs against Luffy/Ace/Iva + possibly Jinbei/Croc + possibly level 6 epic prisoners... LOL
One thing is for sure... once you get the cuffs off of Ace.. ID is fucked as well.
I sort of get this odd feeling that the WG/World Nobels will be destroyed in the first half of One Piece.. and when Luffy and Crew enters the New World.. WG will no longer exist... and just god damn pirates ruling here and there with individual kingdoms fighting to stay intacted. Luffy will somehow play the part of bringing lasting peace to the grandline.