This article explains whether it is expected to see ICMP echo-reply from the SRX, which did not receive the ICMP echo-request.

In the scenarios where, the path towards, ICMP echo-request is sent to the destination from the source is different to the path from where the ICMP echo-reply is received back on the source, the SRX acting as transit in between will pass the echo-reply packets unless it is blocked on the SRX.

SRX will pass the packets as per the flow processing, regardless, whether it has received the ICMP echo-request or not.