I'm surprised no one mentioned the source of cataclysm itself. The fact that there was a civilization and despite all its advanced knowledge - it is now gone.
This would be especially important if Cataclysm was man-made.
Unless the cataclysm was a side effect of the consumption of the easily-accessible fossil fuels. If humanity had to restart its technological progression today with most easily-accessible fossil fuels already used up, it might find it much more difficult to progress past about where we were in the nineteenth century. http://aeon.co/magazine/technology/could-we-reboot-civilisat...
Or they'd just move directly to electrics. Some early cars were electric. The range and power wasn't impressive, but it worked. Wind power becomes pretty obvious at that point as well. Tie a fan to a generator, and voila, free-ish energy.
With no oil, people will just deal with the limitations of low wattage electrics until they get better battery and generation tech. Arguably, you could have a 19th century type society with a nuclear reactor; both uranium and graphite can be mined with simple tools.
If the cataclysm happened in a way that we can easily predict, it would not be that valuable of information. It would be like a dead person coming back to warn you that car crashes can kill people.