A disconnection clause has been created and added to V. Tournament Play and will be added to the OP shortly. Thanks to Shoegazer for the reminder of this missing information.
Disconnections are an unfortunate circumstance, but cannot be fully accounted for. However, there are some stipulations in place that will allow players to mulligan a single attempt for a map. Maps with a player disconnection that occurs within the first 30 seconds, or 25% of the song (whichever comes first) will be nullified and re-attempted. Matches will have a two disconnection limit -- upon the third disconnection, a point will be handed immediately to the player still active within the lobby.
A two minute timer will be placed on a disconnected player when the song played has concluded. When this timer hits 0, the grace period mentioned in PROTOCOL will be (re)activated. If the grace period timer hits 0, the match is forfeited, and the other remaining player will be declared winner. Situations with two player disconnections will be executed similarly to two missing players for a given match: the higher seed will be declared the winner if both players have no time left in their grace period.