The appointment of Ed Grier is not the end of civilization (or Disneyland) as we know it. Grier is an excellent choice to helm Disneyland. He has over 25 years experience with Disney parks, surviving all the tumult from pre- to post-Eisner. That says a lot to me about the man's dedication, loyalty and resilience.
Also, let's not forget that while Disneyland is no longer Matt's park, it's still very much part of Bob's company. Iger's not likely to allow the gains Disneyland has made during the last few years to be squandered, and certainly not with Lasseter and Jobs applying their influence.
While Matt Ouimet will be missed, it's still business as usual at the Happiest Place on Earth. I don't think we have anything to worry about.