My first ever varsity game ended about 2 minutes into the second quarter when lightning came and cleared the stadium. While looking at the radar and the hours long delay incoming, the team that was down 35-0 already decided it was probably a good idea to call it an early night and proposed the idea to the other coach.
Generally speaking, coaches can mutually agree to anything, but the state association may set limits especially if playoff seeding or the like are impacted.