Decisions
It would seem that from reading the recent interviews of Mindy Kaling and Matt Warburton that Danny isn't who Mindy picks in the season 5 premiere. They are making it pretty clear that Danny will always be "in the world of the show" as Leo's dad. They also state that since they are broken up there is only so much real estate, so it makes sense for him to have a smaller role.
Such a shame because the Mindy and Danny dynamic, whether they were friends or romantically involved, was the best part of the show. I found I lost interest in the episodes that didn't involve Danny in season 4.