If two people doing little more than breaking a fence and climbing into a machine can seriously damage your nation's essential infrastructure, that's more on the government than on those two people. Any actual sabotage and there might not have been an infrastructure left to save.

The electrical grid should be able to handle any one power plant shutting down unexpectedly. Ideally it should be able to handle severed power lines and multiple simultaneous failures, with emergency generators for anything essential. Not even because of sabotage, just because power plants are complex machines that can just unexpectedly fail.