I've been fired twice so the band leader could get his mate in. The drummer I'm playing with tonight was fired, from a band we both played in, for exactly the same reason.
Some band leaders will stick with you even if you're shagging their wife and other will sell you down the river at the slightest excuse. That's the life we live in bands. That's why you need to network so you can quickly bounce back and stick two fingers up at these guys.