Sure, Bob is still out of luck though. This only works if Bob also receives an equivalent amount of income through his channel with Alice which is extremely unlikely.
Edit: I speak from experience, working on althea.org which included a similar system (although ours is backed by a blockchain and doesn’t require nodes to trust each other). The reality is that most nodes are either mostly paying or mostly being paid. The channels must constantly be refilled anyway because of this. We found that the saved transaction fees were not worth the complexity, and now nodes just use on chain transactions with no transitive trust system after about 50 cents of debt has built up in either direction.
I follow you people for a long time on /r/darknetplan! How are things going?
As tmacro noted, Offst friends put credit limits on each other. Therefore Bob will not be able to buy forever. This is not really a bug, Bob is out of credits and shouldn't be able to buy more things until he gets new ones.
How does Bob gets credits is another question. In a normal economy Bob would have to get to work or exchange something to get credits.
I agree with you that initially in a small network this could be a problem, because maybe nobody in the network wants to exchange something with Bob for credits. But if this kind of credit system is widely use, I hope this won't be a problem.
Edit: I speak from experience, working on althea.org which included a similar system (although ours is backed by a blockchain and doesn’t require nodes to trust each other). The reality is that most nodes are either mostly paying or mostly being paid. The channels must constantly be refilled anyway because of this. We found that the saved transaction fees were not worth the complexity, and now nodes just use on chain transactions with no transitive trust system after about 50 cents of debt has built up in either direction.