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Depending on how much you drive, the drive train is going to outlast the car. There are a good amount of examples of these lasting at least 300k with good maintenance. There's a couple of ways you can look at this, and it depends on how much work you can do...
1) You could sell it and get something cleaner
2) You could transfer the engine into another Yukon that is good cosmetically but needs an engine
3) You might be able to repair some stuff, but it just depends on how much it is worth it to you
I am assuming you got this for cheap and that made it worth the risk to take on with the rust. Personally, I would either just sell it or drive it till it dies. I don't know if it's a safety issue or not yet, but something to consider with family.
The rockers are basically non existent at this point from the rust, and you do not know how bad the rust is in places you can't see.
Most shops in my experience want a crazy amount of money to do rust repair, and a lot of them don't want the liability. I am sure you can find shops that will do it. But a lot of the rust repair won't be a permanent fix, and is more just kicking the bucket down the road in my opinion.
I got a verbal quote of 3-5K per side just to fix my rockers and rear quarter panel. This is different than frame repairs obviously, but something to think about if you are wanting to do any cosmetic repairs.
Here's the biggest thing: by the time you spend the money to "repair" the rust on this car, you will have enough money to buy a cleaner Yukon that will last longer and be much less of a headache. Most here will recommend buying a plane ticket to the south and driving something back.