1) you are not applying the "do it under any circumstances even with missed bootvector code".
2) the code you implement will, however, work if your program is running.
I don't understand where you set the bootvector to 0xFC in the code above ??? Concerning the watchdog timer, is it launched by 'CALL 0fff0h' ?
The method I apply is to set the status byte to "boot", then let the watchdog reset the uC. This will, with the status byte changed, start the boot code. However, if you do not have the watchdog running already, you need to start it before entering the activation code.

Erik