What are his other stats? Does he have a means of vertical movement beyond himself, because otherwise he's screwed in a cave or more dungeons if any climbing is involved.
Otherwise, since movement isn't "tied" to Strength beyond a character with 0 Str, you're fine; you just need to have high stats otherwise to compensate -- as an Illusionist, I'm hoping you've got some massive Int, Wis, Cha, and Dex numbers, else you're gonna run out of spells, run out of guile, and run out of ways to dodge all the things that are coming at you. And with the way you hit, you might as well be giving the opponent's HP...