It is worth keeping one around.

When the "cloud" is raining and your laptop and phone batteries are drained and you suddenly need to navigate your 4823 times table - its got you covered.

You will also need to work out how to write with a pen or pencil on paper or try and fix up your atrophied ability to remember arbitrary "facts" short term.

Honestly the scenarios where this becomes likely are dwindling with the advent of solar and batteries. Offline knowledgebases and the ability to use them long term are getting increasingly stable, and the likely low point in a societal collapse is probably getting high enough that a slide rule would not be necessary.

I have a Casio fx-991ES calculator, and twenty years later I have yet to need to replace the button cell in it thanks to the tiny solar cell.