That's all super pie in the sky. It's much more likely that Exxon will slowly fade away, with foreign renewables producers undercutting their revenue. And from personal experience with the gov't, it is a total myth that the gov't can't buy foreign products. It just takes more paperwork. Or, (which I've seen firsthand), the gov't buys from a domestic reseller who marks it up.
I'm well aware of the process for doing business with the government. I'm counsel for a billion dollar business that sells almost exclusively to the US government under various rail programs (this includes regional transit authorities using grant money from the US government), and before that I was counsel for a company that did environmental construction projects for the DoD and EPA. There are plenty of ways to do it, but they all cost money, not all of it recoupable through margin. But even with that, who do you think that "domestic reseller" is going to be?
The bottom line is, and I will bet you on it, is that Exxon is not "fading away". If nothing else, they have a fiduciary duty to their stockholders, and if the US government is smart (I know, I know, that IS pie in the sky) they won't be able to continue what little fossil fuel business they do have if they don't participate in broader energy programs. They may not literally sell solar panels in five years, but they are not going anywhere. "AT&T". "IBM". Two companies that have survived (and thrived) after similar transcendent shifts in the nature of the economy. You will be adding Exxon to that list before too long.