COS from H-1B to H4, while in U.S.

[arunka007]

Hello,

Asking this on behalf of my wife. Both of us are on H-1B. My extension was recently approved. Her visa expires in December, extension will be applied in next few months. I am trying to see what our options will be, if this extension is denied. 

1. Can H-1B extension and H-4 COS be applied in parallel?
2. Can we withdraw H-4 COS if H-1B extension is approved?
3. If H-1B extension is denied after I-94 expiry date, will the accrued illegal stay (from I-94 expiry till H-1B denial date) negatively impact future H-1B extensions?
4. Is it legal to stay in the U.S. when I-94 is expired, H-1B extension is denied and H4-COS is in progress?

Thanks in advance for your inputs. 

Regards,

Arun