I've just been in touch with Bob, and had the following from him, with a request to post it here:

Yes it's true!! I've been in London for the past couple of weeks since rehearsals started for a cast change on 16th November so I've had no time to make any kind of official announcement. I was very sad and sorry to have to cancel around 35 gigs to accommodate me being in War Horse but it's an opportunity that I can't turn down for all of the obvious (and some not so obvious) reasons.
I have managed to salvage some gigs including all Pitmen Poets, and the gigs that still appear on my website are all going ahead.
http://www.bobfoxmusic.com