12 players on the field after a timeout

[john_faz]

This one had me second guessing myself. What would you do?

Team A is lined up for a PAT when they realize they only have 10 players, they call a timeout. After the timeout, they line up for the extra point and I blow the ready for play. I begin counting the number of offensive players and hear a player yell "We have 12, we have 12". As I verify that there are indeed 12, a substitute begins running off the field. The snap doesn't happend until after the 12 man is off the field.

I let the play happen without a flag. On second thought, could I have been justified for calling a dead ball Illegal Subsitiution? SHOULD I have called IS? or just let the play happen as no one gained an advantage?

Your thoughts are appreciated.