Okay, I haven't really experienced with the consequences of restarting after losing a battle and the stats are decreased, but here is my question. If your monster dies and you restart will the game remember that your monster died and it will still be dead if you restart? I've averaged out the lifespan of each monster but Cleo always says to retire a good year or so before my average ends. I've managed to still train my Bree a year and 2 months so far after she says to retire. I want to combine my Bree with something but this is my first monster to reach class S and I've got some things I want to do with it first before I have to retire it. Sorry to extend this past the desired question, I'm a bit to extensive with my explanation.

A death is a death to the game. If it dies, it gets flagged. You can reclaim the monster if you restart from a save before the death but the stats loss is permanent.