I agree. You can't argue people into Heaven. If they are determined to be rebellious, there is little we can do other than to pray for them. If you made an honest attempt to share the gospel, you have done what you can do, pretty much. Of course, if this is some person with whom you have regular contact, it is vital that you demonstrate the gospel in your life on an ongoing basis, but I think here we are primarily talking about contacts with more or less random people we meet or street evangelising situations.
As I sat here thinking about this, I remembered an evangelism effort by some members of a church to which I once belonged. It was presented as a survey, the questions being designed to lead into a gospel presentation. As I reflected on this, I realized that this was basically a deception. The would-be evangelists would approach a person under the pretense of doing a survey, when their objective was to present someone with the gospel. It was well-meant, and a clever idea in a way, but was disengenuous.