Emirates leases their planes on 12 year contracts. They do this because they want to have a young fleet. Singapore Airlines does the same. The leasing company might be stuck with the plane after the lease is up, but the airline is not going to care all that much as long as leasing companies are ready to enter into new deals.

Those leases will typically cover the costs of the aircraft, so the leasing company will basically get a 12 year old airplane for free that they can use to generate a profit from (lease, sell or part out) as they wish. Though there does not seem to be any demand for used 380s right now. The one Singapore Airlines has returned (for an entirely new one on a new lease) is currently in storage without engines. Apparently the parts are worth 100 million dollars. It will be interesting to see how that continues to play out when more leases end, since it's unlikely that there will be buyers for say 200 planes worth of spare parts when ony 100 planes are still in service...