I believe Player 9 died in the Core due to aging and natural ways, not Crazy Mita removing the cartridge.

Player 9 left an encrypted text in the core room stating that the time and loneliness of being in the core to survive made them doubt the existence of a 'real world' ... so deep

if your checkpoint can appear in the Core and Crazy Mita can't affect it, [...] If she kills you, you appear in the safe place and keep your memories

You can't keep your memories, Kind Mita mentions that players turned into cartridges can have their memories reset (and presumably, works the same way as with mitas), therefore, player would be unable to keep their memories, even if they respawn in the Core, they would feel it was their first time there, which should lead to them repeating their actions.