Possible departure timeline after I-485 denial

[Arif_1234]

Hi, I am requesting help regarding my current situation and would appreciate any comments. My previous employer filed for my I-140 and I-485 concurrently but I left that job before the forms were pending for ~ 180 days. Eventually, I lost my other valid visa status while waiting for some paperwork from USCIS and I was relying on the pending i-485 to not accrue unlawful presence. I have been planning to leave the US and get back on a cap-exempt H-1B with my current employer. Recently, my previous employer conveyed to me that they are considering the withdrawal of the i-140. As the i-485 might be denied as soon as the i-140 is withdrawn, could you please comment: 

(i) on the time typically taken by USCIS to deny the i-485 after the i-140 is withdrawn (immediate/ some time gap/ varies), when both of them are filed concurrently and the PD is current. 

(ii) whether USCIS would be issuing some form of RFE/ NOID/ interview notice before denying the pending i-485. 

(iii) whether USCIS would give a grace period (by which I could leave the US) before starting to count unlawful presence against me or I will start to accrue unlawful presence as soon as the decision is made. 

(iv) whether I would be placed in deportation proceedings immediately after the I-485 denial or USCIS will allow me a few days to leave the country before issuing the deportation order. 

Given the situation, do you recommend me to leave the US immediately or wait till the I-485 is actually denied and I have the denial notice in my hand. Would it be a big problem down the line (such as visa interviews/ future AOS interview) if I have 3/4 days of unlawful presence in this process. Thank you so much for your help.