I too have been a Mamiya user for a long time, starting with a C2 and a C3.
I use mostly 645 and RZ now. While I hope this is not true, I predicted their exit from the business last year (I hate it when I'm right about those things).
MAC Group (the US distributor) will probably be around a long time and is very good about service and finding repair parts. They also distribute Toyo-View and when the MF market started to tank, they signed on as US distributors for a bunch of other photo equipment.
Mamiya's likely exit is due, I think, to some compatibility issues in the newer 645 cameras and failure to provide viable digital options to their pro users.
Their promised digital camera and back was still not on the market 2 years after being 'announced'. This gives the market a bad feeling. Whether we like it or not, to be able to stay in business, a 35mm or MF manufacturer needs to sell digital in order to provide us with a couple of film camera options.
I checked the Robert White site - most items are close in price to US, but their 'special buy' on new 645 PRO TL kit is a steal - comparable to high quality used prices. This may be a good buy for European or Canadian folks, even though it might take a couple of months to arrive in Canada. To the US, however, is another problem. It may or may not be allowed in by US Customs. It seems the MAC Group actually owns the Mamiya trademark in the US - which under US law, it is technically illegal for a dealer outside the US to sell new equipment directly into the US. Not true with most other equipment - that is simply called 'grey market' - meaning there is no US backed warranty - but this is different.
Anyway, I may try to pick up a spare RZ body or another lens while the used market is still plentiful.
Bob