Do possibly unfounded rumors that Reni might not be playing at the Stone Roses reunion shows count?
Other than that, let's see, some recent Smash-promoted shows include the Boredoms, 22-20s, Blonde Redhead, and Noel Gallagher, so maybe one or more of those acts will return to Japan in July (well, the Boredoms would actually just be staying put in Japan but you get my meaning)? I haven't bothered checking their schedules though, so feel free to point out that so-and-so won't be available that weekend.
The next announcement will probably be 12 midnight between next Wednesday and Thursday. Until then, maybe this promo film will help tide you over (although some of the footage is reused from previous years' promos)...
You only lose your reserved seat. You'll be able to board the next train, as long as you're fine with the possibility of not having a seat (I imagine the shinkansen to Tokyo will be crazily crowded on Monday morning). This will actually be the first time that I use the shinkansen on the return trip as well, due to my friend not being able to secure a decent parking ticket.