Hmmm.... In my experience the most common form is "Well, if the mountain won't come to Mohammed..." meaning "very well, I'll do it myself", I'm not sure how the other way round would work. "Well, if Mohammed won't go to the mountain..." meaning, "very well, I'll do it for you" doesn't make much sense (given that a mountain is unmovable...). Or perhaps you meant some other usage.
That's pretty much the usage I had in mind. It's a figure of speech, it doesn't have to make sense.