A year ago, Microsoft said RPC over HTTP was dead from Oct 31, 2017 and that Outlook clients must use MAPI over HTTP to connect to Exchange Online. The protocol is still dead, but it will persist in a zombie-like unsupported mode. The question is for how long? https://www.petri.com/rpc-over-http-still-dead
Its a shame that it will still work, we have a couple of clients that are very reactive and are running Office 2007. We warned these clients it would stop working come this month (and that they should be migrating off 2007 anyway as its not supported), these guys will just keep using it until something breaks now.
Don't worry. Something will break. But before that. it's likely that a lot more functionality will simply not be available to them.... Why use obsolete clients that are less functional? It doesn't make sense.