What would one do if using EAD working for the same company but I-485 denied? Could one file for I-485 reopen with H1 status expired? Thanks.

I read from immigration chat archives that normally you would want to extend your H1b in case your AOS is denied. But since it is already expired maybe you want to ask for extension with premium processing and then file a new I-485.
I think once your I-485 is denied it will invalidate your EAD. Did you file I-485 before your date becomes current? Was there a reason for a denial? You might want to consult an immigration attorney.