I think what you would end up seeing in reality is that the second-biggest coin on the market, (say, litecoin or something similar to bitcoin that has a significant market share) would take over the market segment while bitcoiners are still trying to figure out how to sync the network over massive interplanetary latency.

This would cause litecoin (or whatever other cryptocurrency) to piss off a lot of earthlings because the latency would get higher for them as 51% of blocks are mined on mars. Eventually litecoin (or whatever) would be as unusable on earth as bitcoin is unusable on mars.

I also say litecoin because the BTC<->LTC atomic swap is one of the oldest and most well established, using the HTLC method, and like bitcoin they are ASIC mined.