My parent have I-94 expiration date May 16 2020. But due to COVID-19 situation could not fly back. We waited to get on Vande Bharat additional flights but could not get seats at that time. Thus, filed extension form I-539. It was delivered by May 11th. I received application back on June 4th with reason for return stating as incorrect fee. Although fee are correct. I sent 3 checks of total $540 ($370 + $85 + $85). I called USCIS customer service and they suggested that may be due to multiple check and suggested resend application with single check $540. By this time we received a call from Embassy of India Washington DC that my parents can fly back on 7th June and we are planning to do so.
My questions are
Should I still need to file for extension of I-94? VISA stamp is still valid till June 2022.
Is there any grace period for B2 visa holder after expiration of I-94?
What are the drawbacks?
Any help would be greatly appreciated.