Yes, it’s been a hot topic in the MacAdmin community both on Mac Enterprise list (oh no it’s the end of the world!) and MacAdmins Slack (told you it was coming, don’t be surprised).
My professional opinion is: “Don’t panic!”
My MacDevOps conference is all about supporting MacAdmins who have been writing code as infrastructure to manage Macs. And do it while replacing macOS Server in the server room with Linux and other OS.
Xsan is staying in macOS Server so I am happy and that’s my main use for the Mac Mini and macOS Server.
I have other Mac Minis doing file sharing for small work groups and moving that out of Server.app in the last revision was unfortunate (it is in the standard OS and usable there but less manageable). There’s also Synology and QNAP NAS for small workgroup file sharing and so much more And many enterprise storage vendors for larger setups.
Imaging has been dying a slow death for years and has been replaced with a thin or “no imaging” concept supported by tools such as AutoPkg and Munki.
Profile Manager is a demo version of MDM and should not be used to actually manage Macs.
Wikis, DNS and Mail should be hosted on Linux, in VMs, AWS, GCP or anywhere other than macOS Server so no problem.
Overall it might be disconcerting to some. But change is constant. And especially at Apple change comes fast and often. We have to get used to it.
Reference:
Apple to Deprecate Many macOS Server Services – TidBITS http://tidbits.com/e/17760
DAM SAN 
Now that Mojave has been out for a few months, curious if you or anyone else has done any testing with it and Xsan. Attempted to migrate an existing server/Xsan configuration from El Capitan to Mojave. This did not go as expected, there were numerous issues with Open Directory and the Xsan service itself resulting in the server crashing/restarting every few minutes. Sounds like Apple is aware of an issue here and currently working with them to provide more info.
I’ve heard mostly of macOS 10.14 Mojave clients on Sierra macOS 10.12 or high Sierra macOS 10.13 controllers. Haven’t tried 10.14 controller yet. Join the action on the MacAdmins Slack #xsan channel for more info and discussion
I think the end of Mac OS has started.
macOS Server is alive. I use it for Xsan. But the good old days of running everything on a Mac Server are no longer. I started MacDevOps:YVR https://mdoyvr.com to help others in the community to move to the cloud and other platforms for server infrastructure.