Sukrim, the actual implementation has more casuistic over what is described in the paper. This is the case for both Ripple and Stellar.

What makes you think that Ripple is not vulnerable to the consensus fault and subsequent reorganization that affected Stellar? (other than the fact that it has not happened yet)

Edit: Consider for relevant discussion, by the inventor of the protocol: https://stellartalk.org/topic/6698-jeds-technical-explanation-of-the-ledger-fork/