I was saddened to hear the news today. Although there have been line up changes along the way, Crowded House has always felt more than Neil Finn + invited session musicians. If it's a one off date, maybe it doesn't make sense for Mark to be involved (didn't some reunion Split Enz gigs not involve Nigel Griggs?).
Also, another of my favourite bands are Squeeze. They've had more line up changes then Enz and House combined. Even since they reformed in 2007, two bass players have been and gone (one of them being from the classic 1979 - 82 line up).
The latest version touring the States at the moment has morphed to a 7 piece, complete with percussionist and lap steel player. The tour is getting rave reviews and it very much still is Squeeze. So maybe too early to write off Crowded House mk whatever number this is yet.
Of course very sad for and will miss Mark Hart being part of it.