I noticed that last night's Imagine... Mel Brooks: Unwrapped used the Arena theme tune during the end credits.
This could suggest that Arena has been quietly axed after 43 years and merged with Imagine.
I don't think it suggests anything of the sort. I think it's more to do with the fact that most of the clips in that programme came from Arena when Alan Yentob was running that, but now he does Imagine. I think Mel Brooks is too mainstream a subject for Arena these days anyway.
There was a new episode of Arena a fortnight ago - http://www.bbc.co.uk/programmes/b09gvgj8