Tricky situation. I'm guessing David was already approached and has not responded yet, refused or perhaps not even asked (possibly at Micks request). He must be getting hounded by media right now.
Despite them separating and going their own way, I cannot believe for a second that Dave or Mick hate each other. I find the situation not dissimilar to family feuds, where you still love the person, but glad not to be around them all the time. I'm certain of the fact that he is supporting Mick all he can. The pressure to have them reform for this must be horrible with it not being in the best of circumstances. I'm struggling to see how any of them would be happy to rehearse and perform any old Japan numbers as they do have enormous professional integrity as well as bridges to rebuild relationship-wise. However, I can see other famous faces making an appearance and doing tribute covers, who can tell?
I don't think David has given any awkward silence. It's well known that he is incredibly private and it's not his style to make his personal feelings known to sate public demand on a website. He best communicates deeply personal issues within his work and I think he is best left to that.