Yep, a rifle shot will comprehensively destroy a transformer. HV transformers are very expensive, very hard to make and if you need any number of them, already have lead times in the years. In fact anything that requires trained personnel, equipment and a supply chain for spares will be out of service indefinitely if the attacks overwhelm the repair capacity. And you only have to injure one linesman or mine one plyon to multiply the difficulty of repairs enormously by requiring armed escort and area sweeping for every repaired pylon hanger.
In any kind of concerted guerilla effort against it, the grid cannot be defended. That said, the first strikes will be easy enough, but anyone who is caught disabling electrical infrastructure or workers after the first few days--once the water, medical and food supplies have gone down and the lethal gravity of the situation is clear--will probably be treated unsympathetically by the locals.
There are also now enough people with solar that it may not be catastrophic. Many of those solar + battery systems have enough electronics to make syncing to grid relatively straightforward.
I wonder how quickly you would see small neighborhood subgrids pop up.
Well, maybe in more affluent suburban areas and rural areas. But in denser cities, the population density doesn't really support that.
Moreover, it's not homes you need to keep powered for critical life functions for millions of people (a few medical exceptions notwithstanding): it's hospitals, food infrastructure (e.g. some very big ovens, sterilisers, fridges, etc), water treatment and so on. Fuel refineries take prodigious amounts of electricity, and those logistics vehicles don't run on batteries yet, and reserves will only go so far. Telecoms also, or how will you order more food, medicine and spare parts? And that's all internet-based now, so you need at least some servers running and a lot of exchanges, towers and cabinets to be working. Ham radio might work to link onesie-twosie farmstead communities, but not for millions of people.
I guess it really depends if it's local, so you can evacuate and ship in supplies like in a natural disaster, or more widespread where there's no external resource buffer.
In any kind of concerted guerilla effort against it, the grid cannot be defended. That said, the first strikes will be easy enough, but anyone who is caught disabling electrical infrastructure or workers after the first few days--once the water, medical and food supplies have gone down and the lethal gravity of the situation is clear--will probably be treated unsympathetically by the locals.