If one part of it's stable you could potentially strap it just to stop it getting worse while you come up with a more permanent solution.

It's far from ideal though but at least it'll stop it falling down while you contemplate the next move which as Tikay says should be knocking it down and rebuilding it.
That depends who owns (or is responsible for) the "good" wall & the "bad" wall.
If (say) Jon owned the bad wall, & I owned the good wall, there is no way I'd allow him to tie his dodgy wall to my good wall, because, almost inevitably, the bad wall will eventually damage, or even pull down, the good wall.