Player 2 has waited 3 weeks and now is not available on the one day offered by player 1. Player 1 has played at the club on the day player 2 had booked as a reserve day for the final.
As others have pointed out, the conditions of the competition are the first place to look, but by sounds of it they do not deal with this specific situation.
Personally, although I understand the view about allowing extensions for the final, I do not necessarily agree with it. If you are going to allow extensions for the final, why have a deadline at all? Or at least put the deadline at a point where you'd have been happy to have extensions until. Otherwise, you could have a ridiculous situation where a player might anticipate a shot or 2 increase of their handicap over the next few rounds, and choose to claim they cannot play by the deadline (only available to play in competitions or at away events to get that handicap up). They could be experiencing terrible form, and want a few weeks to sort it out. And they could be messing with their opponent, who would rather play by the deadline.
Anyway, the Committee need to hear from both sides to be able to decide. It is clear, from what you say, that Player 1 COULD have played the final by the deadline, but elected to play in the competition instead. To me, that would indicate that Player 1 has no right to have the deadline extended (if that was a possibility), and Player 2 should be awarded the win. Flip it around, if Player 1 did play in the final that day, would it be reasonable for him to ask the club to delay the other competition to another date he could play? When I was on Committee at my last club, we stressed that match play events take priority over other club events. So, if players were in a position to pick between one or the other (after all other dates ruled out), then they would either need to play the match play or forfeit their match.