Stay beyond 6 months after I-94 expiration?

Below are the events in the chronological order for my immigration situation.

Apr 3, 2017: H1B Extension/Renewal Filed by the employer

Sep 27, 2017: I-129 and I-94 Expired

Oct 18, 2017: Last Day with the employer

Oct 19, 2017: COS from H1B to H4 Filed

In the meantime, pending H1B extension petition was withdrawn.

Dec 26, 2017: H4 EAD Filed

~ Mar 27, 2018: 6 months from the I-94 expiry

Aug 11, 2018: My spouse I-129 and I-94 expire

My question is:

If my H4 COS is not approved by Mar 27, 2018, would my stay in the US beyond Mar 27, 2018, be legal?