A long time back I wrote two quest based paths to TOEE.
1. The first was: Once the players became aware of the spiders infesting the Delko woods the clock started ticking. Until the quest was completed the spiders in the woods continually increased in number. Once a set number was reached the spiders attacked the village of Hamlet - imagine a horde of giant spiders attacking a village. If the players completed the quest before a set date the village would not be attacked, if the players failed to complete the quest the village was attacked the players could aid in its defense, if the players decided not to defend the village the next time the players visited the village they would find most of its NPC characters slain and the village overun by a horde of spiders commanded by a Drow Priestess and her driders opertating from a base in the former temple of St. Cuthbert with the HP imprisoned in the dungeon below.
The structure of the quest meant that the game could change each time it was played based on the player's actions.
2. The second one was a bit more complex. Basically, the players had 3 choices 1) do nothing, 2) sabatoge the castle construction or 3) stop the sabatoge of the castle. Each choice lead to a vastly different game experience.
Choice 1) Do Nothing. If the PC declined to affect either quest, the outcome was selected randomly. If Outcome 2 was selected (Sabotage Castle Construction) the PCs did not receive the reward, and if Outcome 3) was randomly selected the PCs would encounter a fully constructed castle but would not be granted admission as heros.
Choice 2) Sabotage the castle construction - if completed the castle and its NPCs would not appear on the map of homlett, the PCs would be rewarded, and the village would later be attacked by an army of hobgoblins. There were three ways to complete this quest - each of which had different consequences on the PCs reputation.
Choice 3) Stop of the sabotage - if completed when the PCs returned to the map of hommlet they encountered a fully constructed castle on the map (in place of the construction site) and new NPCs. The Burne and Rufus would treat the PCs was welcome hero's and they would have free admission to the Castle.
In each case the PCs actions had a dramatic effect on the game experience for the players.