Indeed, Zhi Li could only fight to the end; either he became king, or he turned outlaw.
But Duke Turing Tuo was different; he could switch sides and pledge loyalty to Zhi Yan. When the time came, he would still be the first man of the Commander-in-chief's Office, still the top military figure of the Rage Wave Kingdom.
After Zhi Yan's ascension to the throne, as the Regent Royal Consort, Suo Lun would not compete with Duke Turing Tuo for position. For Duke Turing Tuo, the only discomfort was the prospect of living under Suo Lun's influence from then on.
Moreover, if Duke Turing Tuo cast his lot with Zhi Li in a desperate gamble, not to mention the possibility of losing.