Do not know how to reset entities or map after MobArena game

hey i have a quick question of how to reset entities (minecarts in my case) on my MobArena map after a game. this is what happens. i have a railing that goes into a mountain. players in the MA would put a minecart from a chest on to the rail and push it into the mountain. as the minecart travels through the mountains it land on a detector rail, activating some redstone, (not gonna explain all the redstone circuitry) and long story short, it make the ground shake cus of pistons under the map. this works in mob arena but the problem is even after the game is over the minecart is still there and activating the redstone. i would like the minecart to go away after the game and reset for the next game. i would also like the map to reset completely after a game (I.E. blocks that are broken like rails on a block the gets moved cus of a piston so the rail is broken after the block is moved.) any suggestion on how to do these? if anything here needs clarification please tell me.