There are two different risks involved in using your own rifle in Africa:
1) Risk of rifle loss/damage by the airline (scope damage happened to me courtesy of British Airways)
2) Risk of rifle having some mechanical issue/breakage in the field (i.e., the airline didn't lose rifle/ammo)
My reply focused on #2. I get that the .375H&H can be used on PG as one's light rifle, yet double for DG if something broke on his .450 Dakota (which is rather improbable). It's a form of "insurance", though at the cost of carrying a 10 lb rifle which is overkill for everything under zebra/eland vs an 7-8 lb .30-06 appropriate for PG. I understand the choice, though it seems to me a bit "belt and suspenders".
Not necessarily a rhetorical question: What will back up your .375H&H if it breaks? Should you take a third DG rifle, such as a spare .375?
I guess it comes down to every hunter assessing the odds of specific troubles, and the cost of negating such. I'm comfortable taking one quality DG rifle, and a .30-06 for PG. (Before I book for DG, I do inquire if the PH has a spare DG rifle in case of emergencies.) If, for example, a quality DG rifle will survive/perform in 99% of hunts, then carrying only one risks 1% odds of hunt failure (assuming a loaner DG rifle is unavailable). Carrying a backup DG .375 reduces the odds of hunt failure from 1% to 0.01%.
Yes, my Dakota could be run over by the Land Rover, breaking the stock, or some such disaster. That is a 1% chance I knowingly take, just as Nighthawk's 0.01% chance if doesn't take a second .375 to back up the first one. Risk management is a personal thing, and there's a danger of recursiveness (e.g., a 4th rifle in case the 3rd one breaks, etc.). One must call it somewhere.
I wish Nighthawk a great hunt in October, and look forward to reading about it!