What would the Byzantine Empire have to do to survive?

[Robert Vermaat]

I think the Byzantine empire would have survived a great deal longer if they had just posted guards at Yarmuk during the sandstom. If they do this then Umar's army is greatly reduced allowing the Byzantines to crush Islam; which means no Manzikert and no Fourth Crusade. Of course after this they would have hand to withstand barbarian, Venitian and later Mongol invasians.
In my opinion their greatest downfall was their complacency.

Sandstorm? Isn't that a legend? Yarmuk was fought over several days, with only the last day resulting in collapse.
I can't see any possibilty of how the Romans would have been able to 'crush Islam' after winning the battle of Yarmuk. They would have retained Syria (at that moment) but they still would have lost Egypt and the other African provinces. But the Arabs were also busy crushing Persia, which the Romans would hardly have been able (or willing) to stop. My guess is that even if the Romans would have been able to hold on to all eastern territories (which I doubt they could), the Arabs would have replaced the persians as enemies. Islam would never have been 'stopped' by the Romans.