Hi MKT
Nice question.
The scenario you depicted is called “BSC isolation” where BSC lost contact with MSC(all TXCDRS are down),in this case none of the counters in BSC will peg as it is unable to provide any service(Except GPRS if Gb link is not down).
But,if only some A-ters are down,you will definitely get TCH blocking counter incremented & BSC will allot SDCCH as in normal case
Br\\
Bijoy