Let's say we have route of 3 hops A -> B -> C -> D (A pays D). And in the middle of payment (revealing secret R stage) node C disappear from network. In this case B will be not able to finalise payment because he don't know secret of hashlock.
I know that there is timelock, so most probably node B will need to start
closing channel procedure (channel B -> C).
But what is happening with payment? Is it accepted/rejected/hanging? What is happening with A->B and C->D channels? Will they be hanging until situation with B->C is resolved? Or there is some kind of payment cancelation protocol?