Mats, i do not think this game should suffer from any type of exhaustion.
If two people sit down to play the game over the board, they do not have to play the game to the finish, it can played over a few sittings. I do think playing by email though would be best.
As far as mental exhaustion goes, due to the large amounts of different moves available that will arise during the game, this is not fide chess, it is a game on a very large board. One would have to use their intuition and feel for the game, you would have to disregard many moves that on appearance there would seem nothing wrong the move. There would be too many moves to analize, so you would have to do your best.
Would this add a greater element of luck in the game, i would say definitely yes, would this make the game unplayable, i would say definitely not.
I'm not sure what game people play on game courier that would be the closest to Leaping Bat, would it be Cataclysm?
Cataclysm plays on a 16x12 board with 16 pawns like Leaping Bat, but Cata has 24 pieces to LB's 32, so that is a fair difference, and the piece strength also in Cata is greater than LB, so this is probably not a great example, but still it must give us some indication i think.
Amazingly i have noticed that a couple of Cata games have been completed in under 80 moves, another seems to have gone to around 350, if memory serves me correct. Obviously, it appears that Cata is indeed playable.
In the interest of the study of big board games, if anyone knows another large board variant, at least 16x12 board, played on game courier, could you please post to say.