If you go off near a tower, you're in like flynn. I jumped off once, was caught and reprimanded severely. I also knew a kid who jumped off KT22 (the 'new' quad, not the old double) at Squallyworld and his dumb-ass was also busted big-time.
I think it will only de-rail if the chair is swinging like hell when you go or if you upset the counter-balance sufficiently to cause the weight cables to break. I believe the newer lifts are usually better equipped to deal with that than the old Riblet's were. Just one person going off is unlikely to cause a major strain, it's more like if a whole group of people go.
I don't recommend it because it's probably pointless, but I've done it and nobody died. I'll also say that anybody spraying shit about being a new-schooler and not being respected, who goes out and jumps a chair can put two and two together.
SWB