Whether he shows up or not, the tease was a fun addition to the latest episode of Supergirl.
Mon-El visited Warworld himself, and Mon-El doesn’t seem to be going anywhere any time soon, so there’s a chance.
Of course, it’s also possible that the Supergirl introduction of Draaga and mention of Warworld were only meant as Easter eggs for comic fans (such as Coast City).
We’ll have to wait and see whether or not the show does any more to introduce Mongul into its universe.