Assume that the future battlefields are indeed in cyberspace.
If, for the sake of argument, Vladimir Putin could cut off the power supply to London at the touch of a button (resulting, yes, in some deaths, such as in hospitals or on the Tube), then why would he need a nuclear bomb?
And if, for the sake of argument, Theresa May could cut off the power supply to Moscow at the touch of a button, then why would she need a nuclear bomb, either?
In this age of cyberwarfare, nuclear weapons are obsolete.
If you can take down the power supply to London or Moscow merely by hacking into a computer, then who needs a nuke as a weapon, and what good is it as a deterrent?