You could do a simple trigger like this assuming that you aren't using player 12 for anything:
| Trigger |
| Conditions: |
¤ Player 12 brings at least 1 men to location 'Anywhere'
|
¤ Player 1 commands exactly 0 men.
|
| ¤ Player 2 commands at least 1 men. |
| Actions: |
| ¤ Give all men owned by player 12 at location 'anywhere' to player 2 |
That trigger would give ALL of the units for all players that had left to player 2, so if player 4 had left in the beginning and then player 1 leaves, you would be giving player 1 and player 4's men to player 2.
If you want to remove the other players units (besides player 1) then do this. It might interfere with giving player 1's units to player 2.
| Trigger |
| Conditions: |
| ¤ Player 12 commands at least 1 men |
| Actions: |
¤ Remove all men for player 12
|
| ¤ Preserve trigger |
Make sure that the trigers are in this order so that the second trigger will run after the first.