I am not much aware about cell down scenario. Logically, when cell goes down, some or all functionalities may stop. For example: Protocol stack has 5 layers and at the time of cell down, it may be layer 5 has stopped working and layer1 is still functional. It doesn't mean that protocol stack is functional. I am not able to see any benefit if cell broadcasts MIB and SIBs when cell down is in progress and what can be achieved if it does ?