Matt Vogel wasn't available, as he's in England working on the newest Muppet movie to be released next year. Also, Tyler Bunch said on his Twitter account that he most likely won't be performing Herry full-time. So, it's probably not going to be a permanent recast.
Jerry Nelson had an enormous vocal range; I think it would be hard (if not impossible) to find another single puppeteer who can achieve the range of the voices Jerry did. While Matt Vogel has taken on many of Jerry's characters (and worked as an understudy for them with Jerry), I wouldn't be surprised if other performers were also cast for some characters (Tyler Bunch was cast as Thog, another Jerry character, in The Muppets). Herry has a very gruff voice (when compared to Robin, Floyd or Lew Zealand), it may be a hard one for Matt Vogel to replicate. Look at Jim Henson's characters - many of the higher range characters (Kermit, Ernie) went to Steve Whitmire, while the lower range characters (Rowlf, Dr. Teeth) went to Bill Barretta and others went to Dave Goelz (Waldorf), Eric Jacobson (Guy Smiley) and others. Even Frank Oz's characters didn't all go to Eric Jacobson; David Rudman got Cookie Monster.
Oh My goodness Jbrangwyne, you have a point on Vogel working on the newest Muppet movie. Well I hope Vogel is doing fine on the new Muppet movie. And when Tyler Bunch said he won't be doing Herry full-time, do you think this means Herry will still be seen in the background only? Is Bunch not interested in performing Herry? Or when Matt Vogel is done filming the new Muppet movie Vogel will take over the role of Herry along with the Count?
Oh, well we'll just have to wait and see, however I saw this new Sesame Street viral video on the Sesame Street Youtube where they reached 1 billion views. And this new video called Counting the You's in Youtube features the Count von Count performed by Matt Vogel.