I think this 出かけてて actually comes from 出かけている. And 出かけている's continuative form is 出かけていて. And we sometimes omit い because it's easier to say when we speak 出かけていて quickly, so it becomes 出かけてて.(we often say 出かけてる in the same way.)
We don't say 出かけていない (from 出かける+いない) in the sentence because it can have two meanings("he is out" and "he is not out") and we are confused.
And わ is just a exclamation. It has no meaning.(women sometimes use it and men never do)
I hope you understand logic...