We used it for several years after our needs outgrew IRC. From the cloud version starting in 2013, we migrated to the hosted version in 2016, and it was a pretty painless migration and not too hard to manage/update. I think it stuck around for several years after that until the parent org moved everyone over to Slack Enterprise.
HipChat felt like a great featureset-to-complexity ratio. All-in-all good memories :)
First job out of school had me using Hipchat, so when I finally got a job that had Slack, it felt like bloated Hipchat. Didn't think about Hipchat for years until this post and I miss all the emotes/GIFs we used on it.