Is he riding alone or in company? It makes a big difference to all aspects, safety, breakdown assistance, the general enjoyment of the trip.
Make sure that the bike is fully serviced – use fully synthetic oil for best reliability, forks and brakes, chain or belt tensioned correctly etc. Carry good wet weather gear and some emergency ration packs. I use equipment from my boat and carry an Epirb (Emergency Position Indicating Radio Beacon) in case I come off and can’t stand or walk. It has happened once – as well as flares and a satellite phone. I have been right around Australia on bikes and Australia is a very big, very remote country. It is probably already covered, but a digital camera with a spare battery and extra memory cards is a must.
Organise a check in schedule. Make sure that he makes contact at set interval – usually when arriving at the next overnight stop, so that you can get a head start if something happens. Make him set a daily alarm to remind him to make contact. Here (Australia) we have a system when traveling in remote areas where the local Police are informed of departure and expected arrival times.