P9 - 19 are closed from the beginning of Sunday 23rd to early Wednesday 2nd Jan inclusive for the replacement of Battersea Pier Jn. It isn't just closed on NYE.
On a Monday evening all the trains on the Sussex side would have departed before the fireworks are over and the late services are all Thameslink from London Bridge...
Not quite.
GTR and their predecessors have usually operated extra trains from Victoria to accommodate passengers travelling home from the New Year fireworks. These have typically been towards the busiest South London Metro routes and on the Brighton Mainline.
This has applied both before and after the recent cutbacks to Sunday-Thursday overnight trains.
Most passengers will not wish to head as far as London Bridge so I agree it is somewhat concerning that the Sussex side of Victoria is basically completely closed. It risks putting major pressure on last trains out of Waterloo, in particular.
One can only hope that crowd control plans have evolved sufficiently to accommodate this. There are major event plans in place, but I haven’t seen the bulk of them, so I can only hope everyone has worked together properly on this one. It may not be a case of millions of passengers, but ten thousand inconvenienced drunk people at 2am are not going to make for an enjoyable experience...