I have received many notifications from Google saying that Album Archives and Google+ are going away as no one is really using them. In this case, where will all of the new photos from Google Hangouts be stored?
This wasn't really announced, yet. As per the latest news, you are supposed to back up all your photos and videos either via Album Archive or via Google Takeout. Google Hangouts is slowly getting "discontinued" as well. In the 1st phase, this will happen for all G Suit users and the 2nd phase will be rolled out for the rest of the users. Eventually will be Google Hangouts replaced by Hangouts Chat and Hangouts Meet including a few of current futures and bunch of new ones.