。
The train's departure will probably be delayed.
Literal
Train [of-の] departure [topic-は] be-late [probably-だろう].
A compact prediction using the plain conjectural ~だろう ('probably, I expect'). 出発 ('departure') is the noun form — here it's the subject/topic being predicted to be late, rather than the train itself. 遅れる attached to the noun topic 出発は reads slightly stilted but grammatical.