To piggy back on Laitch's comment, let me say that you might as well buy a new bike if you feel you need everything on the bike to be as reliable as new.
While my trips are not circumnavigations, I do get a few days away from home on a bike with 90,000+ miles. I get my peace of mind by riding the bike regularly at home, performing all the maintenance at the proper intervals, and never deferring any required repairs. I think the members here will agree that regular use and conscientious maintenance is the best way to keep these machines as reliable as they are known to be.
My second line of defense is what I cal the "Rescue Box". It is a box of spares to fix problems that may arise during the trip that can't easily be cured at roadside with the few parts I carry. For my trips, I pack a USPS Flat Rate box with the stuff that can kill the bike and can be hard to get. The box has the parts, special tools, and miscellaneous, is sealed and just needs to be addressed to where I happen to need it. I leave it with someone I trust along with the money to cover the postage necessary to get it to me.
For a trip like yours, I would use boxes from a good international courier service. I would have a box for each of the various systems on the bike. That way, you aren't shipping a lot of unneeded parts. Clearly mark each box with an identifying mark and carry an inventory list with you. That way, once you can identify what you need(alternator, starter, ECU, etc) you simply have your contact at the home base address and ship the correct box to you. When the job is done, you can ship the unused parts and tools back home.
Barring a serious crash, I would expect that three or four medium size boxes can support almost any breakdown on your trip.
