This very topic came up in a discussion group recently (God works like that when He wants to get a message through to us...) and another woman pointed out how much hope we can and should have when we clearly know that the answer to our prayer is in God's will. When we pray for something material, our hope is different, since giving us our request might not be in the Lord's best plan for us. He might want us to stay in that unpleasant job, be content with the house we live in, discover a different career than the one we had hoped for, etc. But we know it is always in His will that a person have a good relationship with Him. So we know that as we pray for another person that we are praying according to the desire of His heart as well as our own, and we can have a great deal of hope of seeing that prayer answered the way we would like it to be.
God, who answers prayers, and who wants each one of His sheep to return home to Him, can work in even the hardest of hearts. We may not see all that He does to bring that individual back to Himself, but we can pray with hope, expecting that the person we would like to see in Heaven someday will be reconciled to the Lord and will be with us, with Him, in eternity.