The problem is that attack.js is linked to so many components that you would have to freeze them too (eg, health resistance unitai and possibly others) rendering the game a lot less moddable not just a bit. I'm hoping there is a better alternative but mayber there isn't.
What's slow when Units are dying are the onownership messages and another one. You can see it pretty clearly using profiler2. Making the messages faster might help a lot. Could even be threaded maybe.