Re: Long trip planned-- advice welcome!
If you go with a China engine and it fails, you could still pedal it, but you will still have the additional load from the clutch components, unless you remove the chain.
With a friction drive, you have a choice of what type of engine to use, 2-stroke, 4-stoke, Honda, Mitsubishi, Robin/Subaru, and others. if the motor fails, you could just lift it and lock it in the up position. The only problem you would have with friction is riding in wet weather.
Probably for the best combination of reliability and all-weather riding, a rear rack mounted chain or belt drive setup would be best. You still get to choose the type of engine that you want to use, and the chain/belt can be removed in case of engine failure, and still allow you to pedal.