If you play a level while using a controller, then unplug the controller during the level, you get the message "Player 1 left!" and the player gets destroyed. This leaves you with no players onscreen as the level continues. Despite keyboard and controller both controlling player 1, it doesn't readd the player until you plug a controller back in.
Also - I'm unaware what the status of multiplayer in this version of the game is, but plugging in a controller while a player controlled w/keyboard exists just has you play using the controller for it rather than adding a new one.
23.10.2