So regarding the question of prayer for restoral of lost limbs and God’s will in answering prayer, a few things
If you go online you will find people who say they have regained use of limbs and other body parts (e.g. eyes and ears) and it was done via prayer. Assuming they are correct then it’s fair to say that it is God’s will to allow people to walk, see, hear, hold with their arms.
Apart from some hagiography we don’t have accounts of people regrooving lost legs, arms, ears, or eyes. It’s safe to assume a great many of them have prayed for them, and those prayers were not answered in that way. So it’s not God’s will to regrow those parts.
So the dividing line between what God’s will is and what it is not is to heal broken parts but not regrow them. God is said to be infinite. He could just as easily help a person find their lost keys as he could turn all the lead in the universe into platinum. His ability isn’t prevent the growing of lost parts (or the growth of limbs to someone born without them). No, there has to be another reason – and I’ve never read a good reason why God’s will is split this way.
For the doubter, it’s no coincidence that God’s will matches perfectly with what the body can naturally heal.