Dicey
You should be able to get your EAD in 90 days - question is where do you live? If in NJ - then you\'re a bit screwed. If in NY or MA, then you can go to your local INS office immediately and get your EAD on the spot. However, in NJ, if you don\'t get your EAD in 90 days of the RD of your application, you should be able to go to the local INS office and get your EAD. The main thing is to remain employed for 90 days after the RD of your application.
Now, regarding your shaky position - THAT is a problem. You can plead with your employer to keep you on till you get your EAD. Once you get your EAD, you can change jobs, and ask your employer to keep the I-485 application going. In the mean time, get your new employer to get you a new I-140 and ask your lawyer for advice. However, you have 2 options at this stage:
1. You could be able to apply the new I-140 to the old I-485 application - which used to be OK till recently - it may have changed since then.... check with your lawyer
2. Or if you want to be absolutely safe, simply reapply for a new I-485 - which will naturally mean a delay in the total time.
However, once you get your EAD, you\'re OK for a while. The key thing is to get it.