Ha ha! Imagine the frustration of a player seeing the board morphing first to a hexagonal board, then another player disconnects and the board morphs to standard 8x8 chessboard, then his last opponent leaves and he finds himself over a board of peg solitaire!
That would be really good if we had a crazyhouse version of four-player chess. First you're playing 4-player crazyhouse, then three-player crazyhouse, then two player crazyhouse, then 1-player crazyhouse solitaire... by the time you get to solitaire, the drops would be really annoying.
 
     
     
    
 
      
I don't personally think that solution 1 is a great idea.
If the player wishes to resign because they are losing very badly, the game can be aborted and the good players get no credit.
Ne2willdo, I am not in favour of any of your options.
We should not be inventing new ways of aborting more games.
If you think disconnects are a problem for example, then the best improvement about this will be on the technical side so that less disconnects will happen.
This is why I think the resigned player should lose rating points (like a loss against all other players) like I suggested in the other forum. In that way there is no incentive to abort if you for some reason don't like your position and the others will not have to play a game where some player get the king, some players get easy promotions and some player get between 2 opponents.