Hello Minehut,
I was thinking this would be a very cool and use plugin for kitpvp servers. This plugin prevents players that are combat tagged to run back into spawn when they are about to die.
https://www.spigotmc.org/resources/tagspawnprotection-visual-combat-region-protection-1-7–1-15.6511/
Thank you for considering this plugin. I hope it will be added in the future!