But would the changes brought on by the new capital meant Heraclius would govern or even that Islam would explode?
I'm not sure how moving the capital to a less defensible and less economically critical location would make it LESS likely that Islam would explode.
Presuming a series of wars with Persia is more or less inevitable based on previous history, eventually the Romans were likely to lose one big. They could survive losing big because their city was absolutely unassailable due to a very specific combination of natural and artificial defenses. The other leading cities of the time were less defensible. I'd pick Antioch as a good bet for Eastern capital (IIRC, it had been used that way before) but that is way too close to Persia. Anywhere in the Balkans would have been taken by Huns or Avars before the Persians or Arabs got to it.
Obviously, you can hand wave all the butterflies you like, but the Empire in the East was surrounded by enemies for most of its existence. For much of its existence, it was incapable of stopping a determined attack onto its soil from at least one of those enemies. Repeatedly, invaders got *almost* into the city, but were stopped cold by the defenses. If it wasn't Arabs, it would have been someone else.