Fear of Soviet invasion was real enough in Yugoslavia in 1949, even somewhat in 1950 but later it became more of a propaganda theme. However, I'd say that open conflict was not very likely at the time.

One of the reasons behind the split were Stalins' attempts to achieve a stable relations with West and problems Yugoslav policies regarding Trieste and aid to Greek communists were causing. Invasion of Yugoslavia, even though communist, would raise those tensions much more than Yugoslav intransigent foreign policy could.

Beside, Stalin was sure that his call for "healthy" communist powers within Yugoslavia to topple Tito will be enough to sort that particular problem. In time it became obvious that no such thing will happen, most of Communist party and populace supported Tito over Stalin, and crucially he antagonised Yugoslav war veterans by downplaying their role in Yugoslav liberation. With that, Stalin might have considered an invasion but by 1950 Yugoslavia already got some military aid from USA, Korean war was starting and any open move against Yugoslavia had too much potential for Cold war escalation in Europe.