One cliche that I've seen a few times is the idea that Yugoslavia will always fall into line with the Soviets in the case of WW3, or indeed in the case of any escalation of hostilities - sometimes even with Tito still in charge, despite his personal feelings.
Most likely Tito would do everything in his power to remain neutral until either NATO or the Warsaw Pact had clearly won.
The Soviets would likely only invade Yugoslavia if they have plans to invade Italy (which would make Austria a speed bump too).