I assume that God allmighty is performing miracles right at this moment. He is curing cancer, AIDS, and all kinds of spiritual and physical illness. But, why God doesn’t answer the prayers of a person that has been mutilated? Why there isn’t any miracle performed by our Allmighty God where a limb that has been cut off by an accident or an illness regrows again?
As a general rule, throughout history God has not done such "flashy" miracles except for a definite purpose. Biblically God has done amazing, public, undeniable miracles only during times when he was giving new revelation. Specifically, God worked outstanding wonders and signs at the time of Moses, Joshua, Elijah and Elisha and Jesus. It is not a normal thing, from what we can tell in the Bible, for God to perform a miracle such as restoring a leg which has been cut off. To do so would be to force us to believe. In Luke 16:19-31 is an example of this idea. God is generally not going to work some sort of flashy miracle to get us to believe in him. He has given his Word. He has sent Jesus. He has validated the message of Jesus through the amazing miracles he worked. Like in the parable of the rich man and Lazarus, we "have Moses and the Prophets." I might add that we have the gosples and the rest of the New Testament as well. If people will not believe these things, then flashy attention-grabbing miracles would not convince such people. They will probably have the effect of making us focus on the people rather than on God.
Like you, I wish God would restore severed limbs and cure all cases of cancer, but this is not going to happen. Death and suffering is not the issue. These things will exist. The question is whether men and women will respond to the gospel message. In fact, it is my personal experience that personal tragedy is one of the means by which many people are brought to their knees and become Christians. I believe it is not WRONG to pray for God to restore a mutilated limb, but you should not expect God will do this or put God to the test in this way. A better approach is to trust God and let him work. Perhaps you can pray something like this; "God, please heal my friend from cancer, but even if you do not, please help him to have faith in you and to become a Christian. I pray that your will be done in this situation, and please help me to be an instrument in this situation." I do not mean to give you some sort of formula, but to suggest the general idea. I hope this helps. Let me add one suggestion. At my web site there is an outline and I believe a power point titled "The Problem of Pain and Suffering." You may find this material to be helpful.