In many places, shipping starts to get very expensive. Depending on country, navigating through customs with different language is also tough.

Read journals and you'll find a variety of approaches people have done for things like cracked rims. Most common though seems to be to get to a large city and a fix there. Also in my opinion, when people turn these discussions into frame material type conversations, that seems like a much lower probabilty event than broken wheels.

I did had a frame crack with rear chainstay in Australia. This was midway in an 12 month trip and I didn't have a repair/replace option I liked. I did have a spare bike back in US. At that point shipping a bike was ~2/3 cost of a round trip plane ticket for myself. So I flew back and couriered in the new bike myself.

Prior to my trip across Russia, I left behind a bike with friends, when I did a 1600 mile trip the year before. It was the "hot spare" if something really bad happened like a stolen bike. Only "a train ride" away. Fortunately, I didn't need it. A friend retrieved that bike after first using it to ride the Pamir Highway.