Could bone be replaced by oral bisphosphonates?

Yes and no. These drugs do not build bone but they slow down the body's loss so it can catch up. Some of the pits will refill but only where there has been loss.
Not really. Bisphosphonates (plus serm and new rankl antagonist) slow down loss of bone but still depend upon your own ability to build it back up since bone growth depends upon growth being greater than loss. Only recombinant PTH (known as teriparatide) actually stimulates overall bone growth. Either way, you still need calcium & vitamin d. New study says all are equally effective.