To answer your question, I would regard the area beyond the fairway where one feels the ball is lost to be a ‘lateral hazard’ and then drop the ball according to the current hazard rules. Namely, drop within two club-lengths of, and not nearer the hole than, the point where the ball last crossed the margin of the hazard (In the case of a lost ball, the margin would be the fairway edge) . Not always easy to determine where the ball crossed the margin, but then hooking a shot 200 yds away into a lateral water hazard that runs the length of the fairway poses the same problem at the moment.
However, unlike the lateral hazard rule, add 2 penalty shots not one. So in your scenario, the golfer who hit his shot behind a tree would lie 2, and the golfer who lost a ball would lie 3
Another option would be to adopt Speedgolf rules, but adding 2 penalty shots. See below
They tried this concept on the Professional Bowlers Tour, and it was a huge hit with players and fans. It would be a cool change-of-pace. I always liked the week they used the modified stableford scoring system too. Not something for every week, but one week a season isn't going to mess up anyone's game.
Great clubs. $170 is cheap. I love mine.
Just don't get frustrated with lower trajectories at first. This club with an S300 shaft has a notoriously low trajectory until you get your swing speed up. That said, they're really good clubs, and I think you'll enjoy them as well.