They may not have much arms now, but they have money. There are certainly states that would not mind selling them arms for profit.

While secession will be troublesome, there are not many attempts at preventing secession that have not turned ugly violent in recent years because of attempts to prevent it.

I lived through a non-violent federation split and certainly hope for this outcome elsewhere. In the case of my country majority of the people didn't want the split either. Despite that it was possible to happen without violence.