If millions of people stop paying monthly utility bills, electric utilities start to run in the red, or have to further raise rates while the grid further destabilizes. This is unfolding in real time in California and a few studies have come out showing that subsidized rooftop solar is doing more harm than good without utility-grade energy storage.
I realize that in your scenario we're talking about millions of people no longer paying utility bills, but surely that could not and would not happen overnight, and I cannot imagine that these companies could not find some wiggle room in their billion dollar profit margins to adapt to a change that might for once lower monthly bills.
But that would make actual use effectively free and disincentivize conservation. So it's a hard problem to solve.
You could perhaps raise the effective price of solar by writing in high per-month fees for any houses with solar, but also waive those fees for homes which prove they have a substantial-enough battery solution to help ease demand on the grid during the relatively high-use hours of 5PM to 10PM.
[1] It's different for big industrial users, like factories operating 24/7; their per-unit costs are dominated by consumption rather than infrastructure. They also get lower prices partially reflecting these lower costs.
There is often a difference between "industrial" vs. "commercial" but both seem to pay lower rates than residential.
Phew. I am so relieved. Not a single day goes by when I do not think about how those poor riches manage.