I just returned from a trip and while I didn't stay at Poly we did visit so I can answer your questions based on my observations:
Main pool still open? Both pools were open, although the pool bar at the quiet pool was closed. I'm unsure about the pool bar at the main pool.
Dining impacts? Captain Cooks, Tambu, Kona Cafe, and Pineapple Lanai were open.
Main lodge/lobby impacts? Everything open except Trader Sams, Ohana, and Kona Island.
Monorail availability? It was available (we took it there from MK).
Will we notice many differences elsewhere around the resort? Aside from it being eerily un-crowded and the closures listed above, not really. The tiki torches were lit all around the resort, etc.
I hope this helped. So sad to find out it won't be open when I return in January. We're staying at BLT but were looking forward to taking the monorail over and visiting Trader Sam's/Ohana but oh well.