@Marcos F are you using a policy based VPN on ASA? If so the ASA connects to the first peer, if that fails it connects to the second (backup) peer. It will only reconnect to the first (primary) peer if the second peer fails.
Instead of using a policy based VPN, you could use a route based VPN and use a routing protocol with a metric to prioritise the route to the primary site. If the primary site fails, the FW will a backup route to the DR site. When the primary site is active again, the tunnel will be established and the routes with a higher priority will take precedence, routing traffic over the primary VPN again.
