LL_PowerOffReq hangs because the proprietary binary provided by TI checks to make sure you have a 32.768khz external oscillator so that you stay within the BT certification. If you use the RC oscillator you would theoretically need to recertify the device with the RC oscillator which would be difficult because of the tolerance. The code above is just blocking and thus can be put anywhere in the OSAL system. I tried to get this code to work with OSAL, but BT is too tightly integrated into it.
good luck.