If I remember correctly, Jagger's response to Brian's death when he was informed was, "It must go on".
Brian had become a drug and alcohol problem for the 'working band' and I'm sure personally among the band members as well. Brian (and Keith really,) was an accident waiting to happen. I'm sure they half-expected to hear of his early demise at any moment because of his substance abuse.
Nobody expects a junkie to live for very long. Dealing with a dope-fiend in any money/business/legal related environment is even harder. Must have been mixed feelings when they heard of Brian's death; anger, pain, frustration, sadness etc. From the quote you posted, it sounds like that was where Jagger's head was at regarding Jones. It couldn't have been an easy thing to deal with for any of the band members.
John