Some filaments stick pretty good to Kapton. I used to use Kapton tape on my Makerbot Replicator build plate, back in the day (when 3D printers were so old they had cranks on the side you had to turn to make them work 
).
Gotta think BBL would have gone with Kapton or Delrin instead of the metal plate, if that’d have worked better. The metal plate adds cost/complexity. Yeah, it’s only pennies. But good design teams care about pennies.
I’d glue the metal piece back in place. A little dab of silicon adhesive, maybe.