How would the WRE be able to survive at least until 1453, with the ERE falling sometime around the late 400s or into the 500s at the most?
The WRE for one, does not have to contend against the Arsacids and then the Sassanids, that has to count for something, right? Perhaps the barbarians cross and settle across the Danube rather than the Rhine, or/and Attila deposes the Emperor in the East ala Odoacer?