i can use p2p as wan

Yes you can configure P2P as a backup.You need to add static routes and firewall policies on both the locations for the P2P link

Hello @pradeepjoria ,

Yes this is achievable, All you need is to create a default route or routing to internal resources accordingly. This can easily be managed by the SDWAN feature, an example where two IPSec are in place in the SDWAN is given below, you can replace the second IPSec with your P2P interface.
https://community.fortinet.com/t5/FortiGate/Technical-Tip-Setting-up-IPsec-VPN-Failover-for-Internet-Access/ta-p/273840
https://community.fortinet.com/t5/FortiGate/Technical-Tip-SD-WAN-Rule-Manual-Interface-Selection-Strategy/ta-p/269717

SD-WAN is the coolest way to achieve it.

To achieve redundancy in your setup where the IPsec tunnel goes down when the ISP in the branch office is down, and you want to ensure that the internet or servers in the head office can still be accessed through the IPsec tunnel, you can configure a redundant-tunnel IPsec VPN. Here's how you can do it:

1. Ensure that both the head office and branch office FortiGate firewalls are configured to support redundant tunnels to the same remote peer.

2. Configure multiple VPN tunnels between the head office and branch office to ensure connectivity even if one connection fails.

3. Configure the primary tunnel to use the ISP in the branch office and the secondary tunnel to use another connection, such as the P2P connection.

4. Enable dead peer detection on the VPN tunnels to detect when the primary connection is down and switch to the secondary tunnel.

5. Configure static routes on both FortiGate firewalls to direct traffic through the appropriate VPN tunnel based on the status of the connections.

6. Set up firewall policies to allow traffic between the head office and branch office networks through the VPN tunnels.

By following these steps, you can ensure that even if the ISP in the branch office goes down, the internet or servers in the head office can still be accessed through the P2P connection via the redundant-tunnel IPsec VPN configuration.