In Mark 16 its saying they SHALL recover . So the idea is anyone that was sick those disciples had the sign gift ,that when they lay hands on them they recovered . We are talking about full recovery. Full healing . A sign unmistakable.
Just think about it. You pray for a sick person, and the person doesn't get healed. So you get your nose out of joint with God and you stand up to Him and assert that He is at fault because He didn't do what you thought His Word said He should do.
A New Zealand cartoonist created a clear picture of what that could be. In a recent situation where New Zealand stood up to the United States on an issue, he drew a cartoon depicting a little kiwi (the New Zealand bird symbol) shaking its fist at a gigantic, imposing American Eagle. Get the picture?
If the Apostle John, who leaned on Jesus' breast at the last supper, when He saw the risen, glorified Jesus in his Revelation vision he fell at His feet as if dead, what chance would you and me being able to stand on our hind legs if confronted with our great God in all His glory saying, "Who do you think you are, questioning My sovereignty in this issue?" I think Job felt pretty insecure when God appeared in a whirlwind saying, "Who is he who darkens counsel without knowledge?"
So, all we can really do in the face of God's sovereignty, is to make our request to God, thank Him for who He is, full of grace and mercy, and then leave the outcome to Him. The easy part for us is to be obedience and make our request in faith, believing His Word, and then leaving the difficult miraculous part to Him to do according to His will and not ours.