I´d speculate that it will fail much earlier. Their blocks are still literally empty most of the time and if
the prominent backers of Bitcoin Cash will someday switch their support to a different project
(remember, some of them were also involved in earlier ventures like Bitcoin Unlimited and so on), the
project will fade away or become one of these "ghost blockchains".
I agree on the general importance of a competitive fee market in order to incentivize miners to secure
the network when the block reward becomes negligible.