Devs can not provide an answer concerning the continuation of mining on the legacy chain ... Simply put, a chain lives as long as there are people mining (on) it. A chain lives means that there is a coin. So, either the non-obelsik miners stop mining and then the legacy chain will die, or they continue mining and it will live. Obelisk miners will mine on the hard forked chain (the new main chain). Given the fact that I don't think non-obelsik miners will be willing to throw away their equipment, it's highly probable they will continue mining on the legacy chain.