1

In case we are playing:
1. Game probably took most resources
2. We don't like the game shutdowns automatically

Solution is to set prefered process to kill, when we don't have enough resources. We don't need to game was killed, but plasma-shell is an example, which isn't necessary, when playing.

1. I fail to see why shutting down a process _after_ you ran into resource issues helps and
2. this certainly would be something that has to be implemented on a lower level, not the graphical desktop environment. Because other processes might take much more resources in background, backup jobs for example or software upgrades.

I suggest you simply terminate the process manually before starting to play if your system really runs into issues.