For some reason when I opened up Sibelius 7 today the Aria player didn't show up on the active devices window.
Anyone have any idea what has happened?

Hmm. I'm not sure. You might want to inquire with the folks at Makemusic. They may not help you with Sibelius, but they are the stewards of the Aria player and may have some ideas.

It seems persistence and patience was in order.
Once I updated the Aria player all my problems were resolved. Still don't understand why it suddenly disappeared.
The sequence of events were an update for my computer, which was not likely for the operating system as the current version # did not change after the update. Once that was complete though Sib 7 had this problem. I updated Sib 7 and still no solution. i updated the Aria player and ";poof"; it's back to normal.

Bottom line, it works now.