SSL VPN AND SITE TO SITE VPN

Hello Sachin Chopade,

Thank you for reaching out to the community, as of now there is no auto-failover option: 
There is this settings under the SSL VPN Global settings called the override hostname:

If you leave this field blank, SSL VPN clients establish connections with the WAN IP address of the firewall in the listed order on Network > Interfaces.

Further more you can submit a feedback from the GUI itself:

Hello Sachin Chopade,

Thank you for reaching out to the community, as of now there is no auto-failover option: 
There is this settings under the SSL VPN Global settings called the override hostname:

If you leave this field blank, SSL VPN clients establish connections with the WAN IP address of the firewall in the listed order on Network > Interfaces.

Further more you can submit a feedback from the GUI itself:

OK sir thanks, if i will blank the host name if primary goes down then secondary will work right ? if yes then i will installed sophos client its shown single wan ip in setup  then how it connect cause i have download sophos setup through WAN IP and installed please guide and what about site to site VPN

Yes, if it fails to connect on the ISP which is down, it will try to connect on the another if that settings is kept blank as suggested. 
Similarly the same for the SSL site-to-site as the global settings for the SSL remote and site-to-site is the same !!