Would it be possible to overtake the network by running a secluded mining operation for many years?
'Longer' means 'more total work spent'. You're not going to be working harder than all miners put together are you? Then the only way to get some money is to join the existing miners and work with them. And by doing that you coincidentally enlarge the group of 'honest' miners, making it that much harder for someone else to consider your  'evil' plan.