Hello Alsayed,
as in routers the security associations SA have a lifetime based on two factors: time and traffic volume.
see
IPsec SAs use a derived, shared, secret key. The key is an integral part of the SA; they time out together to require the key to refresh. Each SA has two lifetimes: "timed" and "traffic-volume." An SA expires after the respective lifetime and negotiations begin for a new one. The default lifetimes are 28,800 seconds (eight hours) and 4,608,000 kilobytes (10 megabytes per second for one hour).
https://www.cisco.com/en/US/docs/security/asa/asa72/configuration/guide/ike.html#wp1042781
Be aware that extending the lifetime exposes to security risk so it is not recommended.
the best way would be to have a GRE tunnel encapsulated in IPSec on the ASA originated and terminated on routers with a routing protocol running on it and high metric so that is not used until primary path is active.
R1 ---- ASA1 ---------------------------- ASA2 --- R2
Hope to help
Giuseppe
