and if someone goes travelling around the world by boat for 5 years... and they come back 5 years after 'their' chain has been abandoned? Would the average postman or butcher's wife know what to do?
There's only 'their chain' if they're mining, which is something unlikely to be left alone for five years. If your coins are dormant then all will be fine. By that point all this crap'll be a distant memory and they'll be spendable on the chain that won.