This would SUCK. Badly.
Say I am a Adv. Goon. I have 50 hp left and a chain gunner is chasing me i have 1 leap to safety to make and suddenly it slows down allowing the chain gunner to aim better at me enough for that last 50 hp to go down the drain.
Yes. But you want win, like alien with no spawns? Team with no spawns almost everytime lose. So, you want only lose later or lose in more interesing way (slow down)? O choose last option.
If human have advantage, because other alien die, then it's not so bad because aliens die anyway (soon or later).
If alien have advantage, because other alien die, then it's ok, but they die anyway (soon or later) :-)
Better would be also slow down mouse movement, but that is impossible...
there is no need for a mod at all... just reduce the fps at which the server is running and deal is done (for general time scale). As for single-person after kill... (outcome / effort) -> 0.
Question is, if server fps 10 = nice slowdown everything, or make screen choppy (if that change affect anything - I think client modification is needed).