I've had good quality square taper bb's go maybe 20,000kms, but that one in question at one point was making creaky noises, I took it all out, cleaned out all the gunge and dirt in the threads that had worked in over the years, regreased the heck out of the threads, and it went another few years before making noises again before I replaced it figuring its life has been more than enough.

my take is that a good quality sq taper, installed properly, on a bike that is kept clean and not always ridden in wet, dirt road conditions, will last a long long time.
One factor that probably helps in my case is that Im a light guy, so I dont put a ton of force into a drivetrain, and I wipe off gunge on the exterior of bb areas on my bikes regularly.

I now have a bike that is my first with a external bb, a common shimano hollowtech 2, and this bike and bb now has what must be about 7000+ kms on it. I bought the bike used (not new as I had written before), and stripped the frame, so all of the bb threads etc were cleaned and liberally lubed when I reassembled it, and since then the bike has gone about 6000kms, a good amount fully loaded.
Initially was very skeptical about this type of bb, having heard first hand stories and also being told by trusted mechanics that they dont last as long as sq taper, but probably because of my weight, power output and bike maintenance, I cant say that Im disappointed.

my take on finding a sq taper, or ISIS, is that they will be around, but will there be the axle length you need? Most likely they will be lower quality bb's also....
I suspect also that even in Ouagadougou, most mountain bikes sold will have external bearing bb's now....I can only speak for my limited experience in Latin America, but a good bike store in a city will have all kinds of bb's, disc brake pads, etc.

If your bb went after only 8000kms, I wonder what factors were the cause, and I guess we will never know. What I do know is that a very good quality shimano sq taper like a UN-54 or 55 (cant recall) installed properly, can last a really long time for me, so if I know a bb in in good shape before a trip, I wouldnt be that concerned, especially given that mine was giving indications of sounds long before it was an issue, and even at the end it was still turning very well.

A bike of my wife once had a sq taper bb become slightly loose while on a trip, but I had never touched the bike as it was bought new, and the problem was an easy fix by a mechanic, remove it, clean all the gungy stuff out of the threads, liberally regrease and reinstall with a proper amount of torque.

I'm still wondering how this hollowtech will last, but there is no doubt about it, they certainly are easy to work on.