2G: Roaming when transmission from BSC to MSC disconnect !

[bluep]

Dear friends, pls help me
We put 2G BSC on province, and connect it to center via optical transmission
We're using roaming with another PLMN when weak signal
Oneday, optical transmission is disconnect, BSC die, no service in that province
Some MS automatic roaming , but some not. We must turn off BTS then they roaming
Pls help me why this happen