What happens if R is not revealed by one of Lightning Network nodes? (Payment cancelation) 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?
The situation is less worse than you seem to assume. If node C disappears the channel A,B won't be affected. Also there is no direct need to affect the channel B, C and C, D. So most channels will stay open.

The payment process is a two stage process and it depends during which stage of the process node C disappears to see what happens and how nodes react. 

First stage: setting up htlcs from A to D. If C disappears before the htlcs have reached C the onion /payment is cancelled. No channel will be closed. Otherwise the resolution of the second stage takes place. 

Second stage: preimage is propagated. Node D might force close the channel to settle the htlc on chain. In that case B could also see the preimage on chain an settle off chain. C has time to come back and claim money from B. If C is away too long C will have lost money sich B will have won. If D has settled before C disappears C will not be incentivesed to disappear as C could not get Reimbursed by B.

So we see the only channel that might break in such a situation is the C,D channel. But in any cases only C can loose money / funds by disappearing. This C is Incentivised to stay online and be responsive