Islam as a threat to the Romans and Persians didn't really begin until after Prophet Muhammad died (also he never fought against the Berbers or in the Maghreb). However, it is plausible that the Quryaish kills Prophet Muhammad before he establishes Islam IN Arabia.
If it's before the Hijra in which they kill him, that's it. Islam dies as a minor footnote in history, maybe at most as large as the Druze or Jains.
If it's after the move to Medina, Islam will survive in some form. There are capable leaders such as Abu Bakr and Umar who can take the helm and Islam, at least in Medina, would survive. Whether Tis would be recognisable to the Islam of OTL is very doubtful. I assume the core beliefs would be the same and nothing else.
Also the rise would be much slower as they don't have the OTL base of Arabian tribes to rely on, fighting a much more prolonged war with the Quryaish.
So either an Islam nipped in fhe bud or unrecognisable to OTL Islam.