I think we see a facelift in 2016 at the earliest, Lambo has historically used 10 year life cycles with mid cycle refreshes. Keep in mind, Murci production halted at ~4000 units as a result of demand, not a cap. With demand high for the Aventador, common sense business practice would be to order more molds for the carbon monocoque not start over RD building an all new model. Not to mention, efficiency has increased in production since they started building them in 2011 as a 2012 model year car. There is no way they just stop at 4000. VAG and Audi are all about profits, if customers want Lambo's mainstream models they'll keep them coming.
Rumor circulating a few dealerships is that the refresh may incorporate a dual clutch transmission from what I've been told. Many Aventador owners own other super cars and apparently customer feedback has been strong on the ISR being mediocre at best compared to the dual clutch technology that is now the super car standard. Cost to refresh the appearance, uptick the power and add a dual clutch is nominal compared to the RD of developing an all new model and engine if demand is still present for the existing. There is no reason to believe that the Aventador will have a depreciation curve dissimilar to the Murci over time.