As far as Crispy being a big enough deterrent to Bamber to stop him attempting the massacre, this is very unlikely -
Crispy was not a guard dog.
Crispy may not have woken in the kitchen.
Crispy may have woken but not barked.
Crispy may have barked briefly before recognising Bamber.
It would be unlikely anyone awake upstairs behind closed doors would be able to hear Crispy bark.
There is no guarantee anyone upstairs would bother reacting to hearing a dog bark.
It would be impossible for Crispy's bark to wake people who are upstairs and asleep behind closed doors.