Traditional career paths post post-doc
The reason to do a postdoc is because you want to continue to do academic research.  This might be a short-term goal, or a long-term goal, or exploratory (you're not sure what you want to do long-term).  The latter two are the usual reasons.

Lots of people go into industry after doing postdocs (either because they decided they prefer that or couldn't find an academic job they wanted), so that's no issue.  Keep in mind that it's generally easier to go from academia to industry than industry back to academia.

How long it takes to transition from post-doc to a permanent faculty position depends on the field and type of job you want.  In math, 3-4 years (1-2 postdocs) is normal before getting a permanent research job and 0-3 is common for moving into primarily teaching jobs.

As for "success" rates from postdoc to permanent faculty, I think they're reasonably good, say over 50%.  I quoted some relevant data from the AMS in this answer, though I don't think the right data is there to give you a precise number.  If you take into account that a large fraction of these people want to leave academia, the success rate should look quite good.