First of all, I donu2019t understand why you have to leave the country. If the EAD card was approved that means that USCIS is working on your case and thatu2019s a good reason to not leave the country. The EAD card might have been returned to the USCIS because of the mistake with the address or the delivery person couldnu2019t access your mail box and then sent it back to the sender who is in this case USCIS.Just contact USCIS which your case number or receipt number and explain to them what happened, they will be able to send it back again to you and they will verify the address if this was the reason why your EAD was returned back to them.Regarding your job offer, you can try and explain to them the situation and show them some document which shows that your EAD was approved but just undelivered hopefully they will be able to wait untill you get your EAD card.Good luck.