Routes in a firewall. Gateway decision wireless or ADSL VPN

Hi,

I have a client who now we put an wireless connection to connect two office.

He before had connected the offices by VPN on internet connection

He has two firewalls to generate the VPN and the gateway of the computers is the firewall.

Where I need to put the routes and which routes I have to put to direct the traffic between the offices go forward the wireless and if one of the wireless routers crashes the trafic go forward the VPN

Thanks.


PS::The wireless routers are Mikrotik RouterOS, the firewalls are Sonicwall (SonicOS) and the gateways are routers form the ISP.
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