Try flying over central Africa without Inmarsat - you get a frequency for the next sector, maybe with a friendly reminder that it may take a while to get a response, and then you try for 15 minutes to reach somebody over VHF. There may be an HF frequency you can try, so you do that. No joy, of course also not on guard. Still no contact with anyone, massive CB right on the route, no traffic on TCAS. Avoid it, broadcast on guard and 126.9, eventually you'll be able to reach somebody in the next country. Of course you would never consider diverting in this situation unless you're forced to.