OT Coin Toss = 49'ers Demise?

ilvdsnts said

First of all they played a 15 min qtr., not 10. Second, they would've just continued their drive in the 2nd OT period just like moving from the 1st to 2nd qtr or 3rd to 4th.

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Yeah 15 minutes not 10, but the rules state they play another overtime period if the drive isn’t over. Does that mean they finish the period or if chiefs take the lead then the game is over? Seems like a gray area I interpret it to mean they play a whole nother period…