The dissolution of the Western Roman Empire was a perfect storm of bad leadership, climate change, internal instability, and migrations. Remove any two or more of those and the WRE can at least make it through late antiquity. Having the Goths be defeated at Adrianople in 378 removes Honorius and Arcadia, as well as the internal gothic migrations. Avoid any of the civil wars, especially around 406/407, and the imperial army would be much more able to contain the migrations over the Rhine. Heck, even Majorian succeeding in taking Africa from the Vandals would probably give the empire enough juice to make it through the migration period. If Julius Nepos stayed in power the WRE could survive in Italy. If the reconquest of North Africa in 468 succeeded you probably get a WRE with similar borders to the 3rd Punic War.