Also 5. The governor Justinian sent to Italy after the fall of Ravenna ended up alienating loads of people, causing the Gothic War to flare up in a big way and turning what should have been a mopping-up operation into a decade of highly destructive and wide-ranging conflict.
Whilst sending back Belisarius may be a risk, Justinian could do worse than get a number of Pro-Roman Goths and Italian Romans and choosing one of them to govern Italy, backed by Narses with an army.
Meanwhile Belisarius is given another army, and also allowed to recruit Goths and Romans into it, as a force to continue the reconquest. If they wait out the Plague in Italy and then invade the Visigoths when they're being hit by it, that could offset a huge number of problems, by taking cities, and doing a bit of a Genghis. "Join without fighting, or we'll take everyone in this city as slaves".
Scary it may be, but with Belisarius still potentially being seen as an honest man, and "talk" of the Romans desperate for labour out east, and an example or two, Spain could potentially fall into Roman hands, and rebuild the Roman economy in the east (via importing quite a number of slaves). Heck you could use the same tactic to either have people join as slaves, or join as soldiers. Submit, and provide supplies and men. Resist, and everyone is a slave.
If it works, that'd lead to quite a large army and support network in Spain, that can be redirected at Gaul if needs be. At which point Justinian can probably repeat Italy and establish locals as rulers, with Belisarius as the real power. He is far enough away to avoid a civil war, but in exactly the right place to take advantage of Frankish issues - and so is Narses. They'll likely keep each other in check. Both possibly becoming Exarchs is that is the way the Empire goes ITTL.