AMQSession_0_8#isQueueExist contains dead code creating FailoverNoopSupport for sending queue declare command which never executed. The code was added when support for address based destinations on 0.8 path was introduced.
The callback is created when ExchangeBound for default exchange returns positive reply and assert parameter is set to true. The passive queue creation flag is set in FailoverNoopSupport. Execution of FailoverNoopSupport sending passive queue declare for non-existing queue would cause session close by the broker. It seems that passive queue declaration can only fail when queue is deleted between sending of ExchangeBound and QueueDeclare. Apart from this corner case, the sending of passive queue declare should be successful and client should continue performing its work after receiving of QueueDeclareOk
It seems that FailoverNoopSupport should be allowed to execute