Not to mention the energy supply chain. If the supply chain required to make electronics collapses, that probably also means the energy supply chain has collapsed, or has at least been severely disrupted. That seems far more likely to be damaging and far more quickly that a lack of ability to keep a microcontroller running. If I don't have gas for my car, it doesn't really matter if I can fix it when it breaks down. (And I run out of gas in a few hundred miles, but repairs are required on the order of tens of thousands of miles.)
This is really what I was trying to get it with my first comment. The problems presented by a lack of ability to make new technology are the sorts of problems that take months or years to become critical, but in a true collapse setting, the issues that matter most would unfold in days or weeks.
(I feel like I should point out that I don't think any of this is particularly likely.)
* I was referring to the energy supply chain, not just electricity. Energy as a whole is very much a global supply chain. (And even more than that, it's very globally interconnected in terms of pricing, etc.)
* As a thought experiment, consider completely shutting down the computer manufacturing supply for two weeks. Then consider the same for the energy supply chain. Which of those has more immediate and profound impact?
Keep in mind that I'm not saying that either of these domains is unimportant. Just that society would and has felt the importance of one a lot more acutely and a lot more suddenly.
It's also possible to bootstrap some degree of computing power without an electronics supply chain, but it's also much easier to cannibalize from existing devices (whereas for the current energy supply chain there are fewer things to be cannibalized, besides perhaps electric motors to turn into impromptu dynamos).
Realistically, both will probably go hand-in-hand: we'll use primitive, cobbled-together generators to power primitive, cobbled-together computers; which we'll use to control more sophisticated generators to power more sophisticated computers (and the more sophisticated processes for repairing/building those computers); and so on until we're eventually back to where we started.
Not really, but the idea is sound. There's a hierarchy of control in electricity generation.
* At the bottom level you have microcontroller driven control loops sitting within the plants themselves. These operate on a sub-second timescale and do things like balance air/fuel/etc. flow through the plant to keep it safely running and stable.
* The lowest level loops take their setpoints and controls from a higher level set of controls that work at the level of the generating unit. Those work along the lines of 'generator 1 produce 200MW and ramp to 300MW over the next 3 hours.'
* Above that are control loops run by the grid operator that dispatch plants to match the amount of generation. (And do so in a safe and economic way).
* Above that are (can be) a series of nested power markets ranging in duration from real time, daily, monthly, etc.
* Above that are (can be) long term capacity markets that help ensure there's enough capacity within a grid to serve future load needs.
(So there are a lot of things that might qualify as 'macrocontrollers'. :-) )