So rather than having Arcadius suddenly die in 408, on May 1st 408, the emperor Honorius dies suddenly. Now, Stilicho's position at this point is tenuous but it is by no means untenable. At the same time, the Theodosian line in the west is now dead, and there are plenty of people in both the east and the west that want to see Stilicho gone.
On top of that, there is the little problem of the usurper Constantine III and of the barbarians that crossed the Rhine at the end of 406. By May of 408, Constantine III had sent Scarus scurrying back across the Alps and had set up his own capital in Arles.
Now there are a few ways this could go: there were still Theodosians alive in Spain, which IOTL Constantine had captured and killed that summer. There's also the problem of Alaric who might take advantage of the situation and Stilicho will, in all likelihood, still fall. If Sarus could manage the situation well enough after the fall, he might be able to maneuver himself into getting his own puppet emperor and possibly solicit the support of Alaric. Or the situation may be too untenable and Constantine III is recognized as emperor. How the east reacts to that would be interesting.
Now what does the new emperor do? He has a series of crises on all fronts-the barbarians are on the verge of breaking through his defenses in the Pyrenees, Gerontius will likely still declare himself emperor in Spain, and Alaric is in all likelihood roaming around central Italy. With the backing of the Roman field army in Italy, I can see Constantine himself going to Italy to deal with Alaric, while diverting more forces to his son Constans to take on Gerontius and the barbarians in Spain. How well does he do?
On top of that, there is the little problem of the usurper Constantine III and of the barbarians that crossed the Rhine at the end of 406. By May of 408, Constantine III had sent Scarus scurrying back across the Alps and had set up his own capital in Arles.
Now there are a few ways this could go: there were still Theodosians alive in Spain, which IOTL Constantine had captured and killed that summer. There's also the problem of Alaric who might take advantage of the situation and Stilicho will, in all likelihood, still fall. If Sarus could manage the situation well enough after the fall, he might be able to maneuver himself into getting his own puppet emperor and possibly solicit the support of Alaric. Or the situation may be too untenable and Constantine III is recognized as emperor. How the east reacts to that would be interesting.
Now what does the new emperor do? He has a series of crises on all fronts-the barbarians are on the verge of breaking through his defenses in the Pyrenees, Gerontius will likely still declare himself emperor in Spain, and Alaric is in all likelihood roaming around central Italy. With the backing of the Roman field army in Italy, I can see Constantine himself going to Italy to deal with Alaric, while diverting more forces to his son Constans to take on Gerontius and the barbarians in Spain. How well does he do?