Its HR's responsibly to ensure that all employees work authorization is verified and valid, if there is an audit by HR or ICE and they see that your work permit is expired than the employer and employee (You) would get in VERY serious legal problems and serious fines and you would be terminated and could become problems for you in the furture when applying for a green card (unauthorized employment) , possible deportation on your part as well since you don't have any status since your DACA/EAD is expired. Its up to you to tell your employer that your EAD card is expired and maybe your employer will let you do a "leave of absence" until you have the new renewed EAD card in your hands, but remember if you knowingly know that your EAD is expired than the possible problems above that I listed could happen to you.