The question Software to combine Springpad with Firefox/Chrome is "obsolete" - Springpad shut down, and thus the question isn't really of use anymore (and can't be answered)
What should we do in these scenarios, if anything?
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Sometimes people have locally downloaded old software versions that they can still use (may not apply in this specific case). Or they can get them from 'old versions' or 'abandonware' websites.
I have occasionally and happily gone back to older versions when certain programs became too bloated (or in these 'app times', when the updated app was buggy, starting using annoying ads, or started demanding more permissions than I was willing to give them).
My initial knee-jerk was similar to what Jan Doggen wrote in their answer, because questions shouldn't really become obsolete – lots of old software is still being run.
After looking at your specific example more closely, i.e. a question pertaining to a defunct web service, I'm a little more sympathetic.
But ultimately, what's the point of closing the questions? Doing so doesn't hide the info from anyone that might be searching for it. And the question and its answers can still be good or bad, independent of whether they're currently applicable.
I think we should have a custom close reason for this scenario where software not only is no longer sold or "regularly" available but for all intends and purposes gone. (I would list Geocities as an example)
This Question addresses Software that is gone. It can't be used in any way anymore. Please keep in mind that if a regular user had a copy of the program and could still use it, this close reason does not apply. (Learn more)
That way the question would not count as "unanswered" and people looking for answers for similar problems could recognize the Questions as "not relevant" immediately.
As far as I know closed questions are auto deleted after a while. We want to avoid that for this specific close reason (if possible) because they were on-topic and relevant at the time they were asked.