Mosfet usually fail always on (or catastrophically to the point where there is nothing left of the part)
So if the fan works on the always on output but not on Fan0 before and after the replacement its not untinkable the fault is elsewhere, unfortunately the next part in the chain is the main processor (FAN0 goes straight to pin 90 on the ATSAM4S8C)
To further diagnose verify the part has connectivity from the Gate to R42, from the Drain to Fan0- on the header and from Source to ground. Then (with power on) check if you have a gate signal on either side of R42 with respect to ground when the fan is turned on.
7e51baf8-718b-4112-bf12-47cc46fc8f10-image.png