Even if your thesis is rejected (which is unlikely) you are unlikely lose your job. Presumably you are on a lower grade anyway because you don't have your PhD yet? I know I am anyway - I won't get the higher grade until I give the department my PhD certificate. If you are on a PhD grade, maybe they would just move you down a grade?
Personally I doubt they would do anything. If I failed my PhD, my employers wouldn't know - they are not going to ask me to prove my PhD because they will have to pay me more! Your employers won't know unless you tell them maybe?
Do you have a reason to think your comittee may reject your thesis, or are you just worrying unnecessarily?