Militant resistance cut Nigerian crude extraction by a sustained 200-800,000 bpd since 2006
Trading Economics
Rough calculations based on 2015 numbers:
Deaths averted by shutting in 200,000 barrels of oil per day: 200,000 / 79,784,300 * .379 * 5,950,000 deaths / 12 months = 471 lives saved per month.
For the months when militants shut down 800,000 barrels of oil per day, they saved 1884 lives per month.
Death statistics are probably conservative, so it seems reasonable to round up to 500 to 1900 lives saved per month.