First of all: I think you can only save him if you didn't encourage him to go after the bandits. Second: When you have the nighttime event (with the 2 wolfs bane in inventory) you have to go to the sawmill directly.
this, it's only a choice between Bernard or Logan if you didn't encourage Logan to go the camp earlier. Location doesn't matter.
decided to test it as i was trying to find some new dialog out of curiosity about how certain characters react to things in one-time events and discovered, I was right. I went to the shopkeeper's place and then picked Logan and was able to do the entire event all over again, Location don't matter what you choose does.