What would the Byzantine Empire have to do to survive?

[M. Demetrius]

I can't see any possibilty of how the Romans would have been able to 'crush Islam'

And I'm not sure that even the Eastern Empire would have been motivated to do so. Too much traditionalism still remained for the Romans to have tried to "crush" a religious system in another culture. While they held Christianity to be the state religion at that time, they would probably still have let others keep their own. But we're talking late 7th early 8th Cent AD here, aren't we?