I’m generally against making saves tied into game mechanics, unless the game is designed from the start to function with that in mind. CDDA was built from it’s roots with save-on-quit and permadeath as the save mechanic of choice.
Example of save/respawn mechanics-tied-to-gameplay working well due to preplanning: Dark Souls
Example of why tying save mechanics to gameplay after the fact is a way to make everyone angry: The entire section of bethesda’s forums dedicated to Fallout 4’s ‘Survival mode’, which features saving disabled except for when you sleep. This feature nearly started world war four over how saving ought to/ought not to be implemented and I don’t think anybody came out happy.
tl;dr: It’d be too much work to get right with the current setup.
You’d have to overhaul a significant portion of CDDA’s game style to make a saving feature balanced, reasonable, intuitive, or even remotely desirable by the majority of the userbase. I am not opposed to a new gameplay type, but build the new gametype around the save function, don’t build the save function into the current game.