The HBO app was not removed and is still available for install in the channel store:
https://channelstore.roku.com/details/0529e360dc0e338a1ccad45a874a7dc6/hbo
You can even login to it with your HBO Max credentials, but you wont have access to HBO Max-specific content.
As far as HBO Max goes (HBO Max app/content), you'll just have to wait with the rest of the DC-loving character-named universe for Roku and WarnerMedia to come to terms.
In the meantime, do yourself a favor and snag an Amazon Fire TV 4 Stick for $30 for current and future carriage disputes and app availability/functionality/etc problems/issues...
