"We're not sure if we could get back to our current tech level afterwards" isn't an xrisk.
Yes it is. Right now, we can't deal with a variety of basic x-risk that require large technologies. Big asteroids hit every hundred million years or so and many other disasters can easily wipe out a technological non-advanced species. If our tech level is reduced to even late 19th century and is static then civilization is simply dead and doesn't know it until something comes along to finish it off.
The world still has huge deposits of coal, oil, natural gas, oil sands and shale oil, plus large reserves of half a dozen more obscure forms of fossil fuel that have never been commercially developed because they aren't cost-competitive.
The problem is exactly that: They aren't as cost competitive, and have much lower EROEI. That makes them much less useful and not even clear if they can be used to actually move to our current tech level. For example, to even get >1 EROEI on oil shale requires a fair bit of advanced technology. Similarly, most of the remaining coal is in much deeper locations than classical coal (we've consumed most of the coal that was easy to get to).
Plus there's wind, geothermal, hydroelectric, solar and nuclear. We're a long, long way away from the "all non-renewables are exhausted" scenario.
All of these require high tech levels to start with or have other problems. Geothermal only works for limited locations. Solar requires extremely high tech levels to even have positive energy return. Nuclear power requires similar issues along with massive processing procedures for enough economies of scale to kick in. Both solar and have terrible trouble with providing consistent power which is important for many uses such as manufacturing. Efficient batteries are one answer to that but they require also advance tech. It may help to keep in mind that even with the advantages we had the first time around, the vast majority of early electric companies simply failed. There's an excellent book which discusses many of these issues - Maggie Koerth-Baker's "Before the Lights Go Out." It focuses more on the current American electric grid, but in that context discusses many of these issues.
Now you're just changing the definition to try to win an argument. An xrisk is typically defined as one that, in and of itself, would result in the complete extinction of a species. If A causes a situation that prevents us from dealing with B when it finally arrives the xrisk is B, not A. Otherwise we'd be talking about poverty and political resource allocation as critical xrisks, and the term would lose all meaning.
I'm not going to get into an extended debate about energy resources, since that would be wildly off-topic. But for the record I think you've b...
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.