The best way to save dieing factions at this point is to use force/diplomacy to take land from strong factions and give them to weak ones... Which is to say that you can take land from the Sweboz (for example) or the Romans (if you aren't Rome) and give those provinces to the Gauls.... Of course you will have to repeat this exercise with certain factions, as they might just be too incompetent to defend their lands. Also, when you take the land using FD you will have small armies spawned in each of the territories that you receive, so you should disband those forces before you give the territories to the weak factions, or you will have quite a drain on your finances. The factions that you give each territory to will spawn their own armies in each city as well.