As per diagram you can still optimize your design with full redundancy towards ISP(CE) side via the layer-2 switch and configure the route or path monitor and provide routing redundancy with static and also firewall redundancy with PAN firewall.
as per given info here how you are doing secondary and DMZ failover.
As per understand I can say that if you are monitoring inside /DMZ links then if anyone link fails from primary PA firewall to ASA then you can shift traffic to the secondary firewall (PAN) and secondary ASA.
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