I think a huge part of that depends on how hard the Tuco arc deviates.

Assuming it doesn't, Tuco still kidnaps Walt in S2(maybe by breaking into his house with no Jesse around to use as bait) and takes him to the desert anyway because he's being hunted by the DEA and isn't sure if Walt ratted him out. Walt would have obviously done a better job at selling the poisoned meth to him but it would have been pointless because the twins were coming and according to Walt, ricin has a delayed effect only after a couple of days or so. Even if Tuco dies and they don't suspect Walt, he's still dragged to the jungle.

How would Walt even begin to escape from the jungle with the Cartel having one foot firmly up his ass, I don't know. From what Tuco said, the DEA would never find them where they were going. Barring any unexpected developments, odds are that Walt would have spent a short time as the Cartel's slave until someone from their side masters his cook and they kill him. There's really no reason for them to keep an outside element in their midst when he has nothing left to offer. Also remember the cancer that was still very much a significant problem until all the chemo and that one major surgery. I don't see the Cartel taking all that hassle on just to keep the guy alive.

That's just Walt's fate. Skyler could potentially have a miscarriage with all the shit that would be stirred with Walt's disappearing for that long, Walter Jr. would probably fall into a depression, hell the whole family would be pretty much scarred for life.

tl;dr Walt's kidnapped and taken all the way to the jungle, Cartel keeps him alive long enough to figure out his cook and then they kill him. All this and more in the darkest timeline, available now in my ass.