In my opinion, both 'be going to' and 'will' are used to say something in future.Therefore, either can be used.
Either can be used. But the most likely form, in my view, is
‘I’ll kill you if you dare do that again’ (i.e. the short form of ‘I will’)
This is likely to be said in anger and quickly, e.g. from parent to child, and probably not with the intention of being taken literally. Unless spoken in earnest, e,g, by a Mafioso, in which case the more drawn-out form, ‘I am going to kill you ...’ might better reflect cold determination.
I voted for "will" in accordance with the rule of Condition 1.