Or some sort of pan-European synthesis emerges, which absorbs Germanic (and perhaps also Baltic and Slavic) paganisms into Greco-Roman and other Mediterranean ones.
Greco Roman religion torward late Roman times was in some ways a Museum piece, which everyone (in Rome) paid lip service to but few took seriously. Meanwhile, Norse paganism went down kicking and screaming and quite literally at swordpoint (at least in Norway and Sweden) and with quite a few martyrs and in some cases massacres.
So, I think it would be more likely that certain aspects of Mediterranean paganism was absorbed into a Germanic dominant synthesis rather than the other way around.