The game is not finished yet, so I set the end of the game at the end of the first year (full game will take 8 years before your sentence ends).
However, you can still continue playing without any issue. Your character will age and get different sprite every year, monsters and dungeons will still work and you can fight Mr. White as many times you want.
At the end of the first year, you get a shitty ending (those are just placeholders) depending on your stats and things you did. If you then check the "UNLOCKS" option in the main menu, you will see all the stuff you unlocked and some hints telling you what you have to do to unlock more cheats and outfits.
You only unlock new cheats / outfits at the end of the first year. You can continue playing your save after that but you won't unlock anything new. Also, every save has unique number, so you can't just save two weeks before your game ends, unlock one outfit, load the save, raise different stats and try to unlock different outfit. The game will give you new unlocks once per save.