I've been a guitar player for a few years, but with the departure of the band's bassist, I've stepped up to fill in the low end. It's actually a lot more rewarding and fun than I had originally believed.

Originally, the band consisted of myself and another guitarist, the bassist, and a drummer. Now, we've only got the one guitar player. How can the keyboard player and I work on filling in the gap created by the loss of a guitar?

Thanks. Now, I have to go learn the bassline to "Money."
Have you covering the entire low end, and let the keyboardist cover the midrange with chords and comping, particularly during guitar solos. Normally the keyboardist could do chords with one hand and cover the bass with the left, but the midrange is where the gap will be. That's just my thinking from when I've played with only one guitar.
The fact of the matter is, the keyboardist shouldn't go itno your range at all. Keyboardists need the low end when they're practicing alone and need to fill up the sound, but when he's got you there and it's YOUR job to fill int he low range, he should stick out. Thus, if he's in the mid/higher registers, he can do better things such as using both hands to make more interesting lines and stuff. He doesn't need to use his left hand to play the low end, and thus can use it for stuff that will be funner for him, better for you, and more rewarding tot he overall sound of the band.