Hey Danny,
See, tricky part with ISP redundancy is that if there is isp link failure, other side would NOT know about the new IP, so tunnel definitely would not have been established. Now, one way to "manipulate" this is to create additional static route, but that would only really help for regular traffic, not VPN.
My colleague and I did bunch of stuff for redundant tunnels with harmony sase, let me see if I can find all the notes I took about it.
Andy
Best,
Andy
"Have a great day and if its not, change it"