You're chance isn't reduced to zero; it's simply reduced more because they'd rather upgrade someone who they don't have to worry about a special meal. But they're more likely going to have additional halal meals on a flight to Saudi Arabia.

Do you mean they should have kosher meals or all meals should be kosher? I thought the op's question was whether or meals are halal by default, and the parallel scenario I thought of was flights to/from TLV which are NOT kosher by default; you need to request kosher (except for Elal).