My personal plot for the finale is below.
Rick's group is preparing to pack up and leave. They booby trap cell block with the grenades from Morgan's apartment, and leave a few others behind to act as snipers. The Governor gathers the townspeople in Woodbury and they drive in their vehicles to the Prison. Martinez destroys the guard towers, but don't receive any fire. They move into the field and kill the walkers (you can see in the promo, the dead corpses), they tear down the fences and enter, Allen proceedes to the entrance and opens it, the grenades explode the , Allen dies, Martinez and a few others are wounded. The snipers open fire, killing Paul, maybe Shupert, and some others. The Woodbury Army pulls back and escape back to Woodbury.
Rick's group come back and they salvage the prison bus. Rick sends the weaker members to a safe area (maybe the farm, another cell block, etc) and he, Daryl, Michonne, and others proceed to Woodbury with the bus.
A shootout occurs and someone maybe Daryl drives the bus through the gate. The shootout continues and walkers begin to pour in. Andrea, Tyreese, Sasha, and Milton meet up with them, and leave. Milton volunteers to stay behind, he shoots the Governor several times, severely wounding him. He is revealed to be alive at the end.
The rest leave as Woodbury is in ruins.
At the same time the prison bus could be the bus from the Woodbury wall because they share a resemblance, and if they were going to salvage it from the yard they wouldn't need Daryl in his motorcycle as seen in the photos from the Welcome To The Tombs Gallery.