If the game is designed to have non-revertible changes, isn't it kind of cheating if you return to an old save game to change a non-revertible event?
Isn't it a failed design if you revert to cheating because the game isn't fun if played in the way it was designed to be played?
Well, I don't really know. On the one hand, if you only ever follow one decision path, you'll miss a lot of content. There's a lot of dialog options which you might want to choose just to see what happens. Generally, the snarky options are great examples here. I might want to lip off to the king just to see what the writers did, but I don't want it to be permanent. The thing about non-reversible changes is that they often make you play very conservatively, instead of taking chances.
The freedom to go back and revisit old decisions is also the freedom to see all of the game's content. Depending on how "wide" the game's decision tree is, if you never revisit decisions, you may only see a small fraction of the total content. And that seems like a waste of the creator's hard work.
On the other hand, consequences don't really mean anything if you can wipe them out easily. And then you get into the question of is it worth getting a consequence if you don't like the actions you took to get there. If you feel the actions you took were right and just, should you not then accept the consequences of those actions?
Sometimes though, it's hard to tell what the consequence of your action will be. This is especially true in games, where the information given to you can be limited. There's an example of in Dragon Age in the Dwarven section. You're supposed to pick between two potential leaders. The problem is that you really can't tell what the significant difference between the leaders is. I started helping one leader, then accidentally did something for the other leader that got me stuck with him. And quite frankly, they were both pretty much the same, so I didn't really care and just went with it.
If a game makes some consequences seem arbitrary, shouldn't the player have the freedom to revisit those actions?
So I'm not really sure which way it goes. Personally, I think you should give extensive saves, and let the player decide for themselves. If someone wants to keep to the narrow path, they can easily do so themselves.
Finally, I'll conclude with a quote I've always liked from Lois McMaster Bujold from one of her Vorkosigan books:
His mother had often said, When you choose an action, you choose the consequences of that action. She had emphasized the corollary of this axiom even more vehemently: when you desired a consequence you had damned well better take the action that would create it.
- Lois McMaster Bujold, "Memory", 1996