A funny thing...
By taking the Synaptic package manager and erasing all software related to the Evolution email client, upon restarting the computer. no more graphical interface, but only this good old console.
A possible reason: When erasing the packages, among the details, it was indicated that at least one dependency had been broken... And this without Synaptic warning me beforehand.
My recommendation for Zorin OS users, is not to go on a software deletion spree, as you might remove something you'll regret. With that said, you removed a core dependency component, then lost the GUI. Unless your a terminal wizard, and can re-install the dependency there, you'll have to re-install the OS.
Well...
sudo apt install --reinstall zorin-os-desktop
Call me Merlin.
The dependency is in the Gnome Desktop Environment, which relies on Evolution for Scheduled Tasks.
That explains why after I uninstalled Evolution I still had two Evolution processes running.
Depending on what exactly You have done and what You removed, this can happen (did it by myself in the Past). There are ... I think 2 or 3 Packages with Evolution that are for Data Center Stuff or something similar what the System depends on.
So, when You remove Evolution in the Software Center or You remove it in the Terminal with sudo apt purge evolution these needed Packages will not be affected by the Remove. But when You use Synaptic and You choose every Package with Evolution this will affect them.
See this:
It's already done, a complete reinstallation... no problem on my side.
But Synaptic should have warned me of the danger, which it didn't.
--> an idea for improvement for the software developers.
OK, thanks, got it.
Synaptic is not developed by Zorin.
Some useful commands on its use here:
Additionaly, Synaptic usually states in a Window, "To be removed" -
You need to click on the arrow head to populate what packages are to be removed so Synaptic does indeed tell you, but you need to know how to do this as I have just explained. 
But unfortunately you also need to know which of the packages/dependencies displayed there are better not to remove...
Is there perhaps a list of pre-installed programs/services that you have to be careful with if you want to remove them or that you should not remove? And conversely, what should not be installed because it will break the system, as e.g. wine32?
It isn't just Synaptic, removing things via the terminal can also break the system. I wonder if Stacer is a better option?
Stacer is no longer maintained and probably not solves the problem which packages should be kept.
Personally, I find that the careless use of such programs by inexperienced users leads even more quickly to a system no longer working, because it is even easier to delete or disable required system services.
(I speak from my own experience - many times I have tried to clean up my system in Windows or Android and tried to switch off unnecessary services and unknown preinstalled apps. After that, something usually stopped working and I had no idea what exactly caused the problem.)
On a side note I prefer Evolution to other email clients, and is the only one that allows you to be able to use Corporate mail without having to purchase an add-on like Thunderbird which has become google centric.
I believe it, but I have to write it down once so that the idea can be transmitted.
And maybe take inspiration from: en.wikipedia.org/wiki/YaST
(but, I'm repeating myself a bit...)
Does this also apply to "Recommended" dependencies? I've managed to uninstall Evolution and still reboot normally:
In theory, I like YaST, but in practice however, I found it to be confusing and difficult to use. Even for simple tasks, dropping down to a terminal was almost always easier.
Not that I wouldn't welcome a similar control panel for Zorin OS, but these things need to be well thought out and designed, or they become a nuance more than a helpful tool.
When You uninstall Evolution normally, there shouldn't be a Problem. It seems that the Data server Dependencies are not affected from a normal Uninstallation.
So, when You type sudo apt purge evolution it only removes the Evolution Mail Stuff. When You use instead evolution-common I'm not sure.
It doesn't seem to be a problem, either. I wonder if there was something else being removed for some reason?
@zenzen and @Ponce-De-Leon, the package that Gnome depends on is evolution-data-server
So removing just evolution should remove only the GUI App for Evolution mail.
But, if the underlying libraries were changed to auto installed, then the evolution-data-server package may get listed later for autoremove.
Or, if a person was looking through packages that were listed, like in Synaptic - and checkmarked all packages that bore the evolution- name...
Ah, I see. Nevermind then 
Modular is the way to go - interconnected but independent - so removing one doesn't break the back of another. That's probably a strength of C. But today's programming has become a bit lazy in that respect.
