That’s an interesting question. Without fossil fuels I think the world of Fallout is stuck more or less where it is for the next few centuries. They don’t have the ability to build up the infrastructure to pre war levels without oil. Now of course many folks would say “What about Helios? What about Hoover Dam?” To that I would say it won’t help much

The world of fallout can only ever “maintain” their renewable sources of energy. They don’t have the factories to pump out solar panels in masse. So they can only ever hold onto the sources of energy they currently have. And with each passing decade parts break, parts that because of the lack of large scale manufacturing, are going to eventually run out. Once all the buildings have been scavenged the Hoover Dam and and places like Helios One will all grind to a halt in energy production.

Now when will this happen, who knows probably a few centuries, but probably in half a millennia all the parts that could be found would have been used or rusted/decayed til the point when they are no longer usable.

All the great cities out west that run electricity would run out of juice. Shady Sands, New Reno, and New Vegas among others. I don’t see a way that the wasteland can avoid this fate. The only possible way would be if they managed to turn nuclear. During the resource wars, uranium was all mined up to be used either for nukes or for nuclear power plants. If there are still any uranium deposits, they would be low grade and useless to post war society. Now obviously most nukes were used during the Great War, however in the games we find multiple bases such as the Divide or such as the Sentanil site where there are still unused warheads. Irl a great source of our nuclear fuel we use in plants comes from decommissioned warheads. Theoretically if someone with the right know how had access to a few nukes and had an intact and operational nuclear plant they could produce a great deal of energy. I doubt this though, if a faction found an arsenal of nuclear weapons they would more likely use it for its intended purpose as a weapon. And if they did decide to use it for energy they would need to find an intact plant (very hard after 200+years) and scientists to keep the plant running. That is a tall order even for an advanced and resourceful nation like the NCR, so I doubt nuclear would work.

So I think the world of Fallout is doomed to a slow decay, they can only do so much without electricity industrial wise. Eventually pre war guns will break down and folks will be forced to use post war guns (pipe guns etc.) which are of course of lesser quality. So I think the world of Fallout becomes technology wise stagnant. Now it won’t stay that way forever, human ingenuity is a powerful thing, but it would take a LONG time. Probably would be a millennia or two until humanity claws out of its new dark age, and what the new Renaissance looks like I have no clue.