There's only one block remains before next difficulty and suddenly everybody stop mining and wait for the 14 days to lapse. Let the next difficulty to readjust lower, then everybody start mining again the next 2016 blocks without an increase in difficulty. Rinse and repeat. Of course, not possible in practical..but what if?
14 days is the time taken by bitcoin system during an 'ideal' condition for all 2016 blocks to be mined out. Anything less, difficulty will be readjusted to match the global hashrate to bring it back to 14 days cycle. Anything more, difficulty will be lowered accordingly. Unless my understanding is wrong :S