Splunk does not currently offer a way to export, mirror, or host the docs locally. You are not the first customer to request this feature, and our web development team is evaluating the requirements and technical scope.
There is no batch download of the PDF files for a specific product/version combination (that's another feature request we have made to the web development team), but you can download each manual as a PDF file pretty quickly. Bear in mind that the Splunk doc team constantly makes corrections and updates, so the PDF snapshots can fall out of date even in between releases.
No need to boil the ocean, I'd be happy with ANY type/version of offline documentation working.
Admins can be responsible for putting PDF files corresponding to deployment version on Splunk servers. Just give an option to open version independent PDF file name when docsCheckerBaseURL is unavailable.
Having no help while writing searches is very difficult. The Splunk installs I use have no connectivity to the Internet and because the product comes with no help, it is super tedious to use.