The first two players to go out are obviously 15th and 16th placed... therefore, they can play a one-off match to determine the final position.
If the player disconnects, then you can both call for a re-match. You must however determine if who DCed... it may be that they are losing and deliberately disconnecting... hahaha!... Im sure none of you would stoop so low as to cheat!... anyway, dont forget to add a screeshot to prove who won the match.