Just a wild configuration Idea (did not test it and i´m not sure if this is realy working)
You could provide for your VPN partner the second IP from your backup ISP and based on the VPN Keepalive settings the tunnel would be rebuild right after your partner router detected that the VPN line is down. Depending on the routers of your partners you could be able to tune this a bit by using SLAs.
But as mentioned not sure if this realy works (fast)
Cheers Michael