You could always just export all your company's slack data to preserve it and make it queryable https://get.slack.help/hc/en-us/articles/201658943-Export-yo...

> My company has tons of institutional knowledge locked away

I think your company should start working on that problem ASAP.

That might not be an issue at many big companies, which likely have data retention policies that disallow storing chat history longer than N days.

They really need to make the search better.