From DragonLance Volume 1 (Adventures 1-4) Page 5, titled "Dungeonmaster notes".
I could find no similar quote regarding PCs.
Reading the introduction it appears to me that they have made several steps to try to make it a non-railroad... the adventures are pretty bad railroads nevertheless.
Several NPCs, members of the the Draonarmies appear throughout this adventure. Try to make them have "obscure deaths" if they are killed; if at all possible, their bodies should not be found. Then, when the NPCs appear later, you have a chance to explain their presense. Be creative; think up an explanation for their "miraculous" survival. if this becomes awkward, or your players become suspicious, then let the NPC die, but be prepared to create a similar (but not identical) NPC to take the dead NPCs place later in the adventure. If you are willing to do this, you may eliminate the "obscure death" rule entirely.
I could find no similar quote regarding PCs.
Reading the introduction it appears to me that they have made several steps to try to make it a non-railroad... the adventures are pretty bad railroads nevertheless.