I assume with the Slavs in North Italy the Germans are forced out of the peninsula altogether. What's the butterfly effects from there?
More likely they'd merge. I can see some Longobards heading south (possibly leading to linguistic exclaves of Germanic in Benevento Duchy) but it is more likely that the "Slavic" group that migrates is quite sble to absorb pre-existing groups in the first place.
I like Basileus's scenario, though I think that Po Valley and Greater Slovenia will end as separate states with probably slightly different languages (Germani-influenced Slovenian proper, Romance-influenced Padan-Slavic).