Dealer is something to rely on for some help, but not put your business in harms way by not having a back up. get a backup body asap.
It doesnt have to be the exact same, but one that will do the job as a backup.
I have had the pain you are having and since then, I have 2 bodies, and 2 of the lens that are my main use lens.
It would be nice for me to have a backup to the digiback, but I don't, as I would not buy one thinking this has a chance it will fail during a shoot. Its the equal to all a sudden Velvia film failing as a type of film. Thats why I think Phase makes them very robust to stand the test of time.
After you spend $10-20K for a digiback, you expect it to work without a issue until its course in technology runs out, (or get a better one). And for the first year or 2 you want to back that claim with a warranty.
In these economic times it is hard to say in 2 to 5 years you will be able to replace that back with one that is better and much more expensive. (i could be wrong as I have read someplace that P65+ backs are out of stock/back order). :-)
Bottom line, you had a bad experince you shouldnt have had, and it can happen with any dealer. Not an excuse, but switching a system might not be the end all answer. Mamiya support should apologize and take measure to provide outstanding support in these hard times for the MF market....Although it might be one of the last left with any wall to lean on.