Most times a dogs leg will not heal on it's own especially if the leg is severely broken and not just halfway broken.
If your dog broke it's leg then you should take the dog to a vet so they can put a cast on the dogs leg and take X Rays to see where the leg has broke.
The vet can then put the leg back in it's place to allow it to heal and apply the leg cast to the dogs leg so that it can heal without the dog moving it's leg or dislocating the bone while it's healing.
The dog who has a broken leg might recover from the broken leg with rest without a vet visit however it's very rare that a dogs broken leg will heal up on it's own.
So if you can take the dog to the vet for the broken leg you really should.