If you are defending against a nation state, you should be worried about your staff being bribed, otherwise coerced or worse just being foreign agents.
In properly run networks, BGP hijacks shouldn't have a noticeable impact.
This is it, find a senior network operator, pick up their kids from school, and take them home.
You now have an agent with full access over that network.
Bullshirt. Even AWS Route53 has fallen victim to BGP hijacking. It takes 1 mistake for SHTF