Late file the petition and I-539, should I leave the U.S. asap? : immigration

My buddy is a Canadian citizen. He assumed he was allowed to remain within the U.S. for six months, nevertheless, it is too late when he discovered there’s only one month on I-94, which is on-line (CBP did not inform/give him something about his B-1 expiration date, nor any paper I-94 or stamp on his passport).

On condition that flexibility for late utility on account of COVID-19 (posted by USCIS), he filed the petition and I-539 for EOS on day 179 from his I-94 expiration date. Sadly, the bundle was mailed again with I-797c (rejected) as a result of the quantity of the charges was not paid correctly. He’s contemplating file the petition and I-539 once more.

Ought to he file the petition I-539 once more, stays right here and wait, or leaves the U.S. asap, which is best for him? If he leaves, the I-539 will probably be deserted and denied, he may have 3 years ban. If he stays and waits, which could take 1 yr, then the applying will get rejected, the pending interval will probably be illegal, he may have 10 years ban. I perceive the pending interval won’t accrue illegal presence if the I-539 was filed earlier than I-94 expired, however this isn’t his case.

Thanks to your assist.