I don't think I've mentioned it before, but vinyl wallpaper, especially on exterior walls, is a disaster waiting to happen. The vinyl prevents escape of water vapor to the interior, so the wall cavity cannot dry. Meanwhile, it hides the evidence that there is a problem inside the wall cavity until it has reached disastrous proportions.
BTW, almost all structures can be remediated. I could have put you in touch with contractors in the Bay Area who really know their stuff. And there is a distinct possibility that you actually had insurance coverage for the problem, even if the insurer told you that there wasn't.
Sorry for your bad luck!