if Alice has a payment channel with Carol and wants to pay Bob, Carol acts as a node, charges a fee, and enables payment
I don't disagree with Carol being an intermediary, and for the liquidity requirement. It just seems to me that even if Bob is unresponsive, Carol doesn't have anything to worry about. He will only transfer the bitcoin if Bob has given him the preimage. Otherwise, the condition in their script is not met. In the sketch, I see Carol asking Alice to give him his bitcoin back, but that payment has never happened. In fact, Carol never gives Alice bitcoin, he receives from Alice, and sends it to Bob. (That, assuming Alice wants to send Bob a bitcoin, and the path looks like this: Alice <-> Carol <-> Bob)
