Based on JBH's answer: if things aren't absolutely extinction-level terrible, then it seems to me that the human race can be expected to recover into self-sustaining "local industry" - farming and ranching, printing, masonry, gunpowder, basically 1600 +/- 200 years.  Toss in some surviving knowledges.

Consider Amish and Mennonite settlements.

I think the BEST outlook would have smelting and railroads.  We'd skip over the telegraph and go straight back to land-line-based telephony.  I'm less optimistic about factories, though I'm not sure.

Consider the future-renaissance village: it looks like the stereotypical colonial New England village... but they've also got calculus and arc-lights, and they understand about germs and the sources of disease, they know most of the periodic table, and they can do a lot with chemistry.  They have the Jacquard loom, and take full advantage of water wheels and windmills.  They might have mechanical adding machines (or they'll just use the abacus). They'll have the "optical telegraph" (heliograph).

If you're edging a bit more into fantasy, they could have functioning Babbage Difference Engines and Analytical Engines.