There is a UserVoice idea open for this, but we couldn't wait, so now we're releasing a free and open source utility to migrate from HipChat! Check out the blog post with the details on the HipChat to Teams Migration Utility.
It's not yet complete but nevertheless something you can already try. All feedback and contributions are warmly welcome!
We've now updated the app with some useful features, you can check out the release here: https://github.com/Lombiq/HipChat-to-Microsoft-Teams-Migration-Utility/releases/tag/0.2.0-alpha
And now it's out of alpha! See the release notes here: https://github.com/Lombiq/HipChat-to-Microsoft-Teams-Migration-Utility/releases/tag/v0.3.0-beta
Today's release includes support for importing attachments too! Check it out here: https://github.com/Lombiq/HipChat-to-Microsoft-Teams-Migration-Utility/releases/tag/v0.4.0-beta