1.)As a matter of risk mitigation,if some government/non government hackers cut of mining pools from network through internet disruption
2.)Physical shutdown by fraud/insider work
3.)natural calamity like earthquake.
How BTC network manage 50% + attack?
I am sure these scenarios are well taken care.
Can some one throw light on this dark topic?
Bitcoin doesn't have any measures to counter a scenario whereby a huge portion of the hashrate gets taken out, resulting in longer block times. Bitcoin difficulty has a limit to safeguard huge difficulty drops and it could take a few difficulty adjustments before the difficulty returns to normal.
I doubt there would be a great decrease in the resources used to execute a 51% attack. Mining operations, though concentrated within China shouldn't be concentrated within the same place. Malicious actors, can however use the hashrate to execute any attacks against Bitcoin.