I was proposing that the TC spell didn't exist. A DM that sets up important goals that cannot be achieved is a bad DM in my book. So if TC didn't exist, there would be an alternative.
I don't see a significant difference from TC not existing and the spell or target not being available to the group whether or not it's just labeled as a "different style". The DM always decides the scenario and decides if the group needs to get somewhere that is a mile away or 10,000 miles.
I was contrasting teleport (just as applicable as TC) existing with not existing. It's kind of necessary for me to do so in order to demonstrate that there can indeed be an important distinction between a campaign where teleport does and doesn't exist.
It seems like you're struggling with the idea of a traditional sandbox, and I'm not sure why. The DM typically pre-establishes the state of the world, and then sets the PCs loose in it. The DM only decides the initial state.
The only way the DM would be at fault in this scenario would be if there were only one way to find out about the cult's plot, and it were impossible (without teleport) to actually reach the ritual site in time from that location. However, that isn't the case. It is far more likely that the DM seeds many different ways for the players to find out. Not even the DM knows when or where the PCs will find out about the plot.
Let me try a different example with lower stakes. A traditional 4 class party. Unfortunately, after a few sessions, the cleric player needs to take a hiatus because of circumstances. The DM decides the cleric will remain in the starting town doing the work of the church, until the player can rejoin.
The players recently learned of a new, unexplored continent, and decide to travel there. Unfortunately, shortly after they arrive, the rogue is eaten by a dragon. They manage to slay it and recover his corpse, but the nearest town is a month away by boat.
In the campaign where teleport exists, the players can bamf back, get the rogue rezzed, and continue their adventure.
In the campaign without teleport, unless the DM inserts a convenient NPC who can rez, the rogue is SoL. Of course, the player can almost certainly roll up a new character to play.
However, I would strongly disagree that this is a meaningless difference.