The MAX97220A-MAX97220E provide thermal-overload protection by disabling the amplifier when the junction temperature exceeds 160°C. During a thermal-overload event, the charge-pump circuit is disabled which causes the negative PVSS rail to collapse. You could monitor the negative PVSS rail to determine if the part is active; however, this would require a negative threshold detector. Alternatively, the charge-pump circuit causes the C1P pin to swing between PVDD and PGND. Switching on the C1P pin stops when the charge-pump is disabled, so you could also monitor the positive referenced C1P pin with a comparator and LPF to determine when switching stops.