On average? If two terminators can't kill each other at the same time (no RLs, GL, or plasma guns) ?
(n-1 / n), if n is the total number of terminators. Maximum for one terminator is, of course, n-1. Unless he commits suicide or something.
And now for something completely different:
Am I the only person who was born after DooM and Quake 1&2, and yet still loves them for their wonderful game-play?