I'm kind of reluctant to answer a medical question on here (and I really think you should seek the answer on, say, a site like Mayo Clinic's site,or another site provided by medical authorities).
However, having said that, what might happen to a fractured bone can depend on whether the bone is just fractured (an undislocated fracture) or whether there is also dislocation with the fracture. An undislocated fracture can heal on its own. (I've had a couple, but not involving the foot.) If it's a more complicated fracture it may heal but won't heal "in the right place" unless it's first put back in place (and if that happens there's the chance there won't be fixing it, or else it will take a lot more medical intervention before it can be fixed.
The problem with a foot, though, is that one is always moving it; so there's the chance it won't heal as quickly. It would depend on which bone was fractured.
If it's a dislocated fracture (which can be pretty obvious if it is) it needs to be put back in place (and put back in place correctly ideally) so that it can heal properly. Dislocated fractures can also involve things like nerves being pressed and other hard-to-see complications (not to mention a whole lot more pain than a "run-of-the-mill", non-dislocated, fracture. :) )
The person who knows he has anything at all wrong (whether it's a fracture or anything else) should keep in mind that unless something is healed there's always the risk of complications, sometimes including infection.
Legitimate, authoritative, medical sites offer information on how long some injuries (like fractures) usually take to heal. So again, I'd recommend checking several of those (or at least one or two) for the kind of information you need.
If nothing else, keep watching the injured foot for things like discoloration, swelling in the area (if the initial swelling and any bruising stage are over) - and also fever.
One question I have is how one knows there's a fracture if it's not dislocated and not obvious. Unless the bone has had a simple fracture before and the person knows the feeling, ordinarily certainty that it's a fracture would involve seeing/feeling something "out of place" - which goes back to its "healing wrong" and/or having complications.
So, one more time: Start by checking out the sites of some well known medical facilities/resources.