What happens if an NFL regular-season game is still tied after the 10-minute overtime period?

What is the "Heidi Game" of 1968 remembered for? What is the "Fog Bowl"? In what year did the NFL expand its regular season from 16 to 17 games? In what year was the two-point conversion adopted by the NFL? Which quarterback of the 1960s AFL's Chiefs won Super Bowl IV MVP? Which Dolphins quarterback, a Hall of Famer, never won a Super Bowl despite passing records? Which Bills quarterback led the team to four consecutive Super Bowl appearances? Which Bills backup quarterback led the biggest comeback in NFL playoff history, from 35-3 down against the Oilers in Ja…