Thanks, MB! I’m interpreting your reference to derailleur damage as mostly damage to the derailleur mechanism itself, rather than to the sprockets, rear or front. I suppose it would be possible to pack a spare, pre-adjusted, but even a well practiced changeout would take time, favorable position, light, and a modicum of temporary peace. I’ll look for a durable gear hub with a wide gear range.
As for single wheel cart vs the bike itself, I have to take into account that rmy wife probably won’t be up to long bike travel, but though it would be tough, could probably handle cart travel, if we were forced to abandon the car.
My bike here in SF started out as an early mountain bike (horizontal top tube) with 1.75″ knobbies.” I switched to 1.375″ (compromise) road tires to spare me some rolling friction on paving, but don’t want any skinnier, because there are lots of tracks still in the roads where I rode when working. The Waterfront in SF used to be heavily RR dependent. Skinny tires fall too easily in the groove alongside the rail, and will overrule you at the worst possible moment.
At any rate, I’m not into stump-jumping, or rock-hopping, just cautious travel. “There are old spies, and bold spies, but no old, bold spies.” I figure it’s the same with cyclists.