Well, the textbooks need to be not just destroyed but accessible, and many advanced physics textbooks depend on other math texts and the like. But most of those are wide spread, so this seems like a reasonable assumption. So it may be possible to avoid spending as much in experimentation. But until the 20th century, experimentation was for physics not a massive set of costs. A more serious issue is going to be engineering, but again, an assumption that basic textbooks will be accessible seems reasonable. The serious issue is more how much one can take advantage of economies of scale and comparative advantage in order to get to the point where one has enough free resources to do things like build solar panels and the like.
Moreover, there's a large amount of what may be things like institutional knowledge or simply isn't commonly written down in textbooks. For example, China for decades now has had trouble making their own high-performance jet engines (1), and during the cold war the USSR had a lot of trouble making high-perfomance microchips. In both cases there likely were other problems at play in addition to technical know-how. but this suggests that there may be more serious issues for many technologies than just basic textbooks.
The FHI's mini advent calendar: counting down through the big five existential risks. The first one is an old favourite, forgotten but not gone: nuclear war.
Nuclear War
Current understanding: medium-high
Most worrying aspect: the missiles and bombs are already out there
It was a great fear during the fifties and sixties; but the weapons that could destroy our species lie dormant, not destroyed.
But nuclear weapons still remain the easiest method for our species to destroy itself. Recent modelling have confirmed the old idea of nuclear winter: soot rising from burning human cities destroyed by nuclear weapons could envelop the world in a dark cloud, disrupting agriculture and the food supplies, and causing mass starvation and death far beyond the areas directly hit. And a creeping proliferation has spread these weapons to smaller states in unstable areas of the world, increasing the probability that nuclear weapons could get used, leading to potential escalation. The risks are not new, and several times (the Cuban missile crisis, the Petrov incident) our species has been saved from annihilation by the slimmest of margins. And yet the risk seems to have slipped off the radar for many governments: emergency food and fuel reserves are diminishing, and we have few “refuges” designed to ensure that the human species could endure a major nuclear conflict.