Order of WHERE IN result for PostgreSQL
Short answer: No. 

The only way to guarantee the order of rows returned is through the "order by" clause. 

You have little or no control over how the database chooses to "get at" any of your data, and, therefore, the order in which it gets to those records in doing so. 

You might get lucky and things might come out in the order you want ...   but don't rely on it.