Fantastic story. Very detailed and methodical thinking. Reminds me a little of 'Survive the Savage Sea' by Dougal Robertson! Just about time to break out the bag of oranges and limes to avoid scurvy!
An auxilliary is invaluable, and 99% of the time will never be deployed. Certainly worth testing on a calm day to see it fires up, and that you have the necessary equipment onboard to secure it in so you can drive it from the main console, to refuel it from your main fuel tanks, have 2-stroke oil, and a sparkplug tool to remove the plug if it gets fouled.
Did you put in a call on VHF so someone knew you would be delayed, but capable of making your own way home?