Hasn't sunk yet; haven't seen any official comments yet about this novel situation.
Update: Looks like Spaceflight Now has the explosion at https://www.youtube.com/live/dtmvbQDou4I at about 90 minutes in
https://www.youtube.com/watch?v=DjDFirLcQDM (Everyday Astronaut)
Landing is at about T+06:42.
https://old.reddit.com/r/spacex/comments/7w4pag/americaspace... ("Air Force Didn’t Take Out SpaceX’s GovSat Booster, Private Company Did (UPDATED WITH CORRECTION)")
https://news.ycombinator.com/item?id=16332582 (ibid.)
https://news.ycombinator.com/item?id=16279316 ("SpaceX Rocket Survives Experimental High-Thrust Landing at Sea")
https://www.youtube.com/live/DjDFirLcQDM?feature=shared&t=11...
This is a bit before that:
https://www.youtube.com/live/DjDFirLcQDM?feature=shared&t=11...