I know for VC they will manufacture any part that may be required if one is not in-stock. There was much said about Minerva retaining it's watchmaking roots back in 2004 when Richemont acquired them and Montblanc lobbied vigorously to bring the Minerva atelier into its portfolio. I was very impressed with Mr. Schmiedt's insistence that each depended on the other for success. Frankly, as long as Cabiddu is involved, I cannot see it being otherwise!
It is an interesting, even critical, issue that your post raises. Does Montblanc Villeret continue the Minverva heritage by maintaining an obligation to support their patrimony? I realize that cost will be the limiting factor and, as with vintage V&C, the price of restoring a "simple" timepiece is often far above the market value of the watch itself. This acts as control over the amount and type of restoration work so as to prevent the shops from being overwhelmed. Still, if they at least offer restoration services for vintage Minerva timepieces then the answer is most reassuring. Is this not also consistent with the mission of the Institut Minerva de Recherche en Haute Horlogerie?
Let's hope the response to a similar question in 2009 hasn't changed: montblanc.watchprosite.com