I think Blake's decision to leave his dad behind was the right one; Neil was literally on his last leg and wouldn't have had the (physical) wherewithal to walk/take another step. Blake simply resolved to leave him by the (camp)fire so he wouldn't get colder and weaker.

I believe Blake was right to leave his father behind, since Neil was exhausted and wouldn't have had the strength to keep walking. That's why Blake made the decision to leave him by the (camp)fire - so that he wouldn't get any colder or weaker.