In a recent interview with Moscow’s state-run Russia-1, a clip of which circulated widely on social media Saturday, the newly appointed Colonel-General Andrey Mordvichev said that the war “will not stop here [in Ukraine].”
“If we are talking about Eastern Europe, which we will have to, of course then [the war] will be longer,” he added.
I highly doubt Germany wants an all-out war with Europe, so Austria-Hungary would be largely alone if they attack Serbia.