There is an export option for HipChat so if you could write an importer for that the migration would probably be straight forward. We also have customers who insist on having control over their data so we are looking into mattermost as well.
Re:Slack Is Buying HipChat from Atlassian
by apple4ever on Friday July 27, 2018 @10:34AM
(#17626239)
Gotta say, I love that the CEO is commenting here.
Mail us at info at mattermost.com? // and this is an open invite to any HipChat users who want to keep data under IT control.
Regarding importing from HipChat, while it is tricky as the data is within HipChat's VMs and not documented, we can potentially work with you to move over smoothly.
The good news is if you switch to Mattermost we run as a single Linux binary with MySQL or PostgreSQL, so using us you have 100% access to your data as well as the source code to understand everything we do with the data.