I think there is likely a problem that the hotel is struggling to relocate everyone - it's likely 400 rooms per night plus numerous meetings and events. Hyatt central are supposed to be contacting everyone, although I would prefer to work directly with the hotel in finding a solution. It would seem sensible that people were contacted in the order of stay.
I hadn't been contacted so rang the normal number and was put through to customer care in the US. After going back to the hotel and asking for in-house reservations, I was informed that there was a choice of hotels (including IC Park Lane, which has the same owners) and that they would see what was available for my dates. Then, if we wanted to choose to stay elsewhere they would possibly contribute to out of pocket costs. For us, it is more a problem that we don't have status elsewhere. To add the cost of breakfast and dinner really makes the stay a lot more expensive.
With regards to fault, it is way too early to say, but I would not think a gas explosion was due to a hotel's negligence. Presumably if this was the case it would invalidate any insurance claim, something no hotel can afford to happen. I would guess it is more likely to be due to London's ageing infrastructure. I am unsure which restaurant was renovated recently - the Montagu hasn't changed as far as I can see and Locanda Locatelli is an independent restaurant, not run by the hotel.
I think there could be better communication between hotel, HGP and guests with upcoming stays, so that people are not simply told that their reservation is cancelled or that he only option in the Andaz. However, I think people also need to think through the logistics of relocating so many people into equivalent hotels in London (I guess this is pretty much limited to Marriott, Hilton and ICs on Park Lane) at the same time as the investigations into the blast, managing staff for the next month or so and trying to get the hotel up and running again as quickly as possible.