Dan does not believe flopping exists.
To answer your question, does B1 need to get killed to draw a charge?
No.
If you judge the bail out was trying to keep from getting killed, and that contact by A1, that results in the train wreck was still through B1, call the charge.
If you judge it as that little belly forward, fly back, before contact...that Dan feels never occurs...and A1 goes down after, call the block.
We get paid for judgment, there is no clear cut, cookie cutter rule to apply, we have to see the play and make a call.
Sometimes the best call is the one we don't make.