Abbott is too much of a coward to request a double dissolution because he knows he'll lose. The Governor General could dissolve the House of Representatives without a DD or he could dismiss the PM if he feels that parliament has lost faith in him or whatever. But then we'd probably end up with Pyne as PM.
Not sure at all that Pyne will be appointed. If supply is blocked, merely switching heads won't solve anything. The precedent, if supply is blocked through the Senate, is to appoint the Opposition Leader the PM. Of course, that precedent is highly questionable. I think directly dissolving the House of Reps is more likely. This will be a HoR-only election, as barring a double dissolution, the Senate operates on fixed terms.