Removing the Discard Changes option on pages is one of the worst design decisions Microsoft has made for quite some time.
This is a showstopper for us. We have over 100k SharePoint sites with hundreds (if not thousands) of authors. This regression will cause major issues across our business.
Note: The latest Microsoft Lists rollout into SharePoint has been a nightmare for us with a multitude of thing breaking, including our List column/view formatting breaking, and users being able to remove filters we had applied to views, etc. But this change has an even worse impact.
Scenario (and an extremely common one)
We have flows (reviews, approvals, etc.) that run when a Page (Standard Page or News Article) is published. Now, if I go into a published page to check on some of the page layout and make some temporary changes (VERY frequent that this happens across all of our authors), I am now forced to restore the previous version to remove my changes, which will inadvertently move the page back into Draft mode and need to be republished. Republishing it again will kick off another flow, and the page will now be published by the user that temporarily updated the page, and on the current date/time. We absolutely need our pages and news articles to keep the actual date they were published and display who originally published them (these are displayed on the page) and not kick off additional review/approval flows.
It will also affect our version history which we rely on for auditing purposes. Before, I could go in and help someone with their page and discard my changes, or our authors could just play around with the design of the page and not have any intention of keeping their changes. Now, those users will end up in the version history when they didn't actually have any intent on keeping their temporarily changes.
You said the versioning solution will work the same as discard changes - but that is absolutely not the case.
I really don't understand the overall Microsoft (lack of) quality control, design decisions, impact assessments, etc. We also don't recall seeing anything about the removal of discard changes in the Microsoft Service Announcements which is a major issue in itself.
I would love for this rollout to be stopped but assume it's not possible at this late date. However, the Microsoft design/engineering teams really need to look at redesigning the co-authoring solution so users can truly discard changes. You said it's not possible, but that's just because Microsoft designed it like that - it's definitely possible. If I'm co-authoring and I discard changes then the other author will just see all my changes removed.
Another option would be to have two modes that you can select from.
- Single authoring mode where the author selects single authoring mode (locked to just that user similar to how check-out works now) and the author can still discard their changes.
- Co-authoring mode where the user selects co-authoring mode, and you can have multiple authors without the ability to discard changes.
We could then go into Single authoring mode to make temporary changes and discard as we do now. Seems like a simple solution to me and would provide the best of both worlds.
EDIT: I also noted this in the announcement:
You do not need to do anything to prepare for this update, but you may want to let your authors know about this new capability.  
We absolutely need to prepare. We need to let our users know that they will no longer be able to discard changes on their pages.