A Peplink Youtube video illustrates how failover occurs when the WAN cable is unplugged. Will failover occur if WAN is still active but ISP is down? i.e. are pings to the www a part of the test to determine if WAN is up or down? I ask because I have an RT-AC68U which advertises ping as a test case but it does not properly detect inability to ping.
Yes failover will occur if isp is down but WAN is UP. There are a bunch of health check methods of which ping is one, but also DNS lookup and http tests too.