I've had many people come to me for prayer, thinking they've fallen away and that there's no longer any hope for them. Although I do believe there's such a thing as a dead man walking, I also believe that it doesn't apply to the one coming to Jesus in repentance. The person who feels as if they've fallen away beyond hope, has been lied to by the devil and they've believed the lie. These people wouldn't be asking for prayer if they'd fallen away completely. We see in scripture how the dead man walking is the person who delights in wickedness without a repentant heart.
2Thessalonians 2:9-12 shows us this truth.
The coming of the lawless one will be in accordance with how Satan works. He will use all sorts of displays of power through signs and wonders that serve the lie, and all the ways that wickedness deceives those who are perishing. They perish because they refused to love the truth and so be saved. For this reason God sends them a powerful delusion so that they will believe the lie and so that all will be condemned who have not believed the truth but have delighted in wickedness. - 2Thessalonians 2:9-12