Put your comments and suggestions below. This is my prediction for the plot in the finale.
The group is packing up and preparing to leave, before leaving completely, Rick booby traps the cell block entrance with the grenades from Morgan's apartment, and leaves snipers behind, my guess is that they'll be Michonne and Maggie. Rick sends the weaker members of the group back to a safe location most likely the farm, a town, or just a spot off the road, maybe even another cell block.
In Woodbury the townspeople are gathered by the Governor, and they get their weapons and leave in a convoy of vehicles that includes the National Guard trucks, the Governor's white trucks, etc. Everyone in the town goes accept for Tyreese, Sasha, and the other unable Woodbury citizens. Milton and Andrea I believe are tied up.
The Governor arrives and they kill the walkers in the field, and they enter the main area after bursting through the gates. Allen proceeds to open the door and the grenades detonate, killing him, and wounding the others behind including Martinez. Michonne and Maggie proceed to shoot and they kill several members of the Governor's army. Shupert is struck multiple times and collapses, dead. Several other Woodbury soldiers are killed, and Maggie and Michonne begin to target the Governor. The duo run out of ammo temporarily giving time for the Governor and the others to escape.
Tyreese/Sasha (either one) stumble upon Milton and Andrea and free them, they make their escape, but Milton volunteers to stay behind with the intention of killing the Governor.
The prison group comes back, and they formulate a plan to strike the Governor, they salvage the prison bus and as they begin to head to Woodbury, Rick spots the group of Woodbury defectors. They enter the prison and Rick sends them to where the rest of the group is.
Milton obtains a gun and readies it as the Governor and his men begin to arrive. He hides to avoid the Governor from seeing him.
Rick, Daryl, Michonne, and some other Prison group members gather outside of Woodbury. They sneak into Woodbury and a shootout ensues, several Woodbury guards are killed, and Glenn is shot, moments later Daryl burst through the front gates with the Prison bus the other Prison group members in the back,
Walkers begin to pour into Woodbury, the Governor is on the street with, a wounded Martinez who is providing cover for him. Daryl spots them and opens fire, with the crossbow and kills Martinez, the Governor shoots Daryl in the shoulder, as he gets closer to finish him off, Milton emerges and shoots the Governor, Daryl runs leaving him for the walkers.
I know the grenades is a little far fetched but I don't think it would be walkers, because I know with 100% certatinty that the group returns, they wouldn't flood the place with walkers if they were going to come back.