After a bit more research, the Airbus view is:
Alert height is a height defined for CAT III operations with a fail-operational landing system.
Above AH, a go-around must be initiated if a failure* affects the fail-op landing system (* list as per AFM)
Below AH, the approach will be continued (except if the AUTOLAND warning is triggered).
The AH is evaluated during a/c certification. Operators are free to select AH lower than the one given in AFM but not a higher value.
and, as the ILS receiver failure would set off the AUTOLAND warning, the correct answer - on an Airbus - to Q3 would be to Go-around.