Since the calibration happens about 100 us before the start of the packet, you do not need to worry about temperature changes between calibration and transmission in your scenario. For the scenarios where this is an issue, such as devices in continuous Rx (lasting many seconds or more), you can rely on FSC_LOCK signal.
We have never measured how much the temperature can change before the PLL goes out of lock, but we believe that you can normally tolerate changes of at least 10 degrees C before you go out of lock. We can not guarantee this number, though.