Currently the PKGBUILD doesn't specify any depends for the fallback support in cinnamon. When cinnamon crashes it tries to launch metacity and mate-panel OR gnome-panel OR tint2[0][1].

I tested on my box here and gnome-panel doesn't quite work on its own. At a minimum you need to install nautilus so it doesn't immediately segfault. This may be a packaging issue with gnome-panel, I don't know. Beyond that, there are no applets and the panels will just be blank and useless as a fallback session without possibly many more depends. I didn't test mate-panel. Considering that, I suggest that we add metacity and tint2 as depends for fallback support.

Fallback support can be tested within a cinnamon session by launching Melange by either: right click panel -> troubleshoot -> looking glass, or use super + L shortcut. From melange actions menu there is an option to crash cinnamon. When this happens the fallback session should be loaded, and a dialog asks if you want to restart cinnamon. Without these dependencies no window manager or panel are loaded. Cinnamon will restart properly, but if it has crashed because of a persistent issue then there will be no fallback.

To summarize:
I suggest adding metacity and tint2 as dependencies. They can be optdepends, but without them fallback will not work as intended.

Thanks for your time.

[0] https://github.com/linuxmint/Cinnamon/blob/61b1d4a2b3f53d98d3d29f3a258012f342ba9e30/files/usr/bin/cinnamon-launcher#L6
[1] https://github.com/linuxmint/Cinnamon/blob/61b1d4a2b3f53d98d3d29f3a258012f342ba9e30/files/usr/bin/cinnamon-launcher#L24