There is a crossover just west of Angmering Station so they could turn there. Sure it has been done in the past. I can see some shuttle between Angmering and Brighton being put on but with Southern not having enough capacity to handle the football traffic. Can't see them putting on a shuttle...
Interpreting the Southern site is a gamble.
Coastway west - you would assume that there should be trains from Angmering to Brighton but looking at the other issues, not sure if the LA to London services will run.
Mainline - It looks like no services into Victoria but the rest says...