I did see a post somewhere from Lasergun (I think) about closing swap for new coins but allowing those with untouched old coins to swap after the deadline. I could support that. Not the same as checking for dead accounts but if I understand correctly there is a record of when coins are moved/created. If that was an option I would say have a deadline for late swap too.
You are right:
As an exception, I will let the people to swap after the January, 2017, if their old coins were not touched after the block #1990382 and we will have remaining the new coins.
But this will be possible only if somebody will still support the old chain (2 nodes + mining).