Are you postulating a 'vanishingly improbable' combination of faults, or what? If the primary problem were the exploding of C1, then no 'fuses' (whether real fuses, destructing resistors or necked tracks) would operate until after the damage had been done. On the other hand, if the primary problem causing R1 to destruct were something other than the explosion of C1, then, as I said, it would surely be incredibly improbable that C1 would simultaneously explode, wouldn't it?The necked track doe not protect the capacitor. If that explodes then aluminium foil and other debris will be all over the place in side the casing and over the PCB. The risk of this foil bridging from 230 volt side to 5 volt side is very high.
Kind Regards, John