If it was a Magneto the bike would have continued running, altenators work slightly different.

efi bike will stop as you are taking main power away from ecu,if it was a carbie bike thay normally will run.

I dont know if it is the same, BUT if you take away the battery when then engine is running on a boat, you can bugger up the regulator! so you may also want to check this!

What a strange thing to do ?
You would have disturbed the main feed from the Alternator to the battery which inturn feeds all the electrics.
Most carby HD's from the last 20 years or so also use electronic ignition, so would die as well.