We suppose a bit more earlier notice would have been preferable, but to be fair Google did announce their plans 3 months ago. For those who have been using the service up until today or more recently, Google has a support page where you will be able to find out how to download and save your chat histories, and also how to backup photos and media files received through Allo to Google Photos.
Allo was originally announced at Google I/O a couple of years ago where from what we could tell, was Google’s way of giving consumers a new platform to chat on, especially with the company starting to shift Hangouts towards enterprise users. Unfortunately it seems that Allo never quite took which led to Google’s decision to shut it down. In the meantime Duo, Google’s video and audio call app, is still very much alive and well where Google even launched a web client for it.