What do you think? What's your preference? Do you like being saved?
As a player, I dislike it. I want my GM to be skilled enough to make me believe the event was going to happen anyway--and it just happens that the event saves our behinds, even if the GM is saving us and had no plans for the saving event to occur.
As a GM, I try never to pull this type of thing. But, I've certainly misjudged the strength of encounters before, especially before I'm comfortable with a new game system. I certainly don't want to kill off the PCs willy-nilly--especially if it's my fault for making the encounter too hard.
I mostly GM in our group, and when we sit down to play (I'm acutally running a game tomorrow), I try to have the session planned and ready to go, giving myself room to ad-lib should the players do something unexpected. And, I always try to have a few light contengency plans. I don't put a lot of work into these, but I do have an idea of what I can do should the PCs go in a direction that I'm not prepared for them to go.
For example, tomorrow, I expect the session to revolve around combat and exploration. So, I have the entire dungeon planned out, and I'm real comfortable with it--as I like the dungeon to feel like a living place rather than bad guys waiting in a room to fight whatever comes through the door. Sometimes, my dungeons will have all the action take place in just one or two rooms because, as the game played out, the entire inhabitants of the place came to where the noise was taking place and ended up fighitng the PCs.
My contingency plans for tomorrow's game has to do with the PCs reaching the outside of the cave. I don't expect this to happen, but you never know how a game is going to go. Once they get out, they've got, basically, three directions they can go. Directly East is where they'll want to go--back to their village. But, in that direction lies a lot of danger. The PCs know this because they came through it to get to where they are now. I think they'll not be too eager to go through that territory again.
But, if they do, I've got a single NPC I've made (and will duplicated him in the game, as needed) in case I've got to pull something out of my butt.
If I need to buy time, I've always found it easiest to spring a combat scenario on the players. This eats up time, is fun, and buys me time to end the session, go home, and better prepare that direction for next time. During the game session next, the goal is to make it look like everything that happened was supposed to happen--no matter what. But, since I didn't get "stuck" last game, I was able to go home and make up some cool stuff for the direction the players did take.
I don't think the players will go North or West because, well, that's the direction of the bad guy's territory. Plus, it's in the exact opposite direction of their home village.
But, just in case they do....I've done the same thing as I did with the East. I made up exactly one enemy NPC, and I will use him and duplicates of him while ad-libbing an encounter if the PCs go that direction. Combat will typically ensue...and, boom! I've bought time to prepare that direction for next game session.
The third way to go, South, is the way I expect the PCs to go. I've set up an enounter there and put a little more meat on it than I did for the others. With regards to the game, that will be the most rich, story-laden way to go.
So, any way they do go, if they get that far next game session, I've got combat for them--which buys me time to develop the direction they end up going in-between games.
EDIT: Out of curiosity, what game system are you using that you hate?