The grid actually already has a fair number of (non-software) circular dependencies. This is why they have black start [1] procedures and run drills of those procedures. Or should, at least; there have been high profile outages recently that have exposed holes in these plans [2].
You'd be surprised. See. GP asks a very interesting question. And some grid infra indeed relies on AWS, definitely not all of it but there are some aspects of it that are hosted by AWS.
This is already happening. I have looked at quite a few companies in the energy space this year, two of them had AWS as a critical dependency in their primary business processes and that could definitely have an impact on the grid. To their defense: AWS presumably tests their fall-back options (generators) with some regularity. But this isn't a farfetched idea at all.
Catastrophic data loss or lack of disaster recovery kills companies. AWS outages do not.