They may back out the way they came in, or wait for another player to come in on a second track, and the two will leave at the same time, on the same track. XOR gates make it so that if a player comes in, another player cannot go through the other track. Positrons and electrongs collide with each other in a flash, effectively restarting each player. If they go through a NOT gate, they flip allegience- positrons become electrons, and electrons become positrons. Not realistic, but interesting.
Polarity causes magnetization to have opposite effects.
Bit showers occasionally happen. The entire grid has a bunch of waves appear, which strech out to the nearest wire, and then follow tracks for a while before they eventually die out. While on the tracks, they magnetize it in various directions. The game should be very fast paced, rather random, and should require constant attention to the details and manipulations. Mastering a board should take a while.