Think Monday morning I would be on the phone to my legal team and get them to talk to BMW HQ.
Bypass the local shop as they are now on a cost cutting duty to themselves and are not interested in your BMW experience.
Explain to BMW HQ the response from the local shop and let them explain the National BMW view of customer care and after sales service.
I would also get your legal team mention the withdrawal of the loan bike and explain you will have to hire another bike as a replacement and charge them for it as its a business asset for your company.
Don't think you have much to loose tbh going forward, And by the legal eagles getting involved they will know are not standing for the dealer B*llsh*t.
PS you could always ask BMW HQ to deal with the local dealer now as you have no faith whatsoever with them after the last conversation ?.