Ancient pre-Christian Europe while pagan,still had various pagan religions. You had the Classical Greco-Roman pantheon,Slavic paganism,Norse-Teutonic pantheon,Druidism,Finnish paganism,Sami shamanism,Basque mythology,Scythian mythology,Thracian mythology,various sects and mystery religions in those religions. Not to mention gods,demons and new beliefs introduced from North Africa,Iran,Caucasian Mountains,Huns,Mongols and Roma. With Abrahamic religions either butterflied or neutralized,you might either see a huge rift because of the different ways of worship,or more likely adoption of beliefs and hybrid religions. Romans were notorious for this and I could easily see the Vikings adopting Druid,Slavic or Finnish gods,maybe even some Tengrism. But it does not mean a religiously tolerant Europe.