Maybe as an option, but speaking personally, I absolutely hate it when a game will only save at specific checkpoints...
Second/thirded. But there is an alternative...
Limit saves by time, e.g. once every 10-20 minutes. Once you save, you can't do so again until the timer expires. That adds a level of tension to the game (since you could face having to replay up to 10-20 minutes if your party perishes) while not limiting players to arbitrary checkpoints.
I would say that "campaign mode" would be a real misnomer for an Ironman-style feature though as it implies more of an extended scenario option. Perhaps a name like "Short-Lived Sourcerer"?
