Two MPLS Sites with a P2P. How can one site handle MPLS failure at another?

Some BGP routing assistance requested.

Ultra High Level Topology: https://imgur.com/a/6LCbA Picked one network from each site for example.

I have two branch sites that send lots of site data to their sister site so a P2P between them was purchase. L3 Switches at each site acting as gateways, peering OSPF with each other and their routers. Routers redistribute BGP to the L3 Switches (There are other WAN connections at these branches for partnered companies). Switches currently not licensed for BGP.

Right now the routers only advertise their site's networks into BGP. What's the best practice to have these router's advertise the other site's networks in case of a MPLS failure at one site. If I redistribute OSPF into BGP at each site the router would send both sites network into BGP at the same cost right?

Thanks!