You also need to look at the cost of not having the engine. If they are going to be short of spare engines for a significant period (I assume one does not just go to the engine store and buy a new one off the shelf) then the potential cost of that will be factored in. The same with the airframe, if they don't have a spare then a future failure may well disrupt schedules and end up costing them more. In itself it's a form of insurance.
The insurance company probably only covers the airframe/engine, not the consequential loss, that's usually clearly excluded in pretty much any insurance policy unless a much bigger premium gets paid.