Serbia doesn't need Russia for the military part, they have enough goons on their own.

The key thing is, if had Kyiv fallen, do you think that the Western nations would have had time and resources to care about the Dayton accords and intervene again? I seriously doubt it and I'm pretty certain the Serbians came to the same conclusion.

Thankfully though, Kyiv held up, and the Serbians were forced to cancel their plans since contrary to expectations the Western nations did manage to get a reasonably united response against the Russian aggression.

The problem remaining is that ethnical tensions still are high and there's not much effort being done to defuse them, partially because everyone's attention is on Ukraine at the moment.

Local sentiment supports your view as well. Lots of my friends and family (hi from Sarajevo) hold belief that if Ukraine had fallen within couple of days there would be war here.