Considering how popular carriers are now (compared with the decline of the 70s and 80s) I find it hard to believe the Invincibles won't be sold to other navies for further service. Unlike the previous generation of steam powered CVs that were sold widely around the world (ie the Colossus/Majestic class and the Hermes) which officially weren't built to last(!) the Invincibles were designed on the 'upkeep by replacement' principle, and indeed all three have been constantly updated over the years so that apart from the hull and super structure very little of the original ships' equipment remains. Anyone buying the ships may be getting a 25+year old hull but all the important 'stuff', engines (gas turbines are replaced regularly, indeed Invincible changed one whilst UNDERWAY during the Falklands operation), wiring (replaced at their last major refits) Radars (regularly updated and in some cases replaced with more up to date systems), accomodaton (now including facilities for female sailors, satellite phones and internet connections for the crew to keep in touch with home, and satellite TV! A far cry from conditions even in the 80s) is as close to new as possible.
Also, the JSF will fit on the Invincibles lifts and hangars as British influence on the design has kept the dimensions down (with an eye to future export sales, no doubt), so I would not be surprised if the sale of the ships was part of a package deal with F-35Bs in a similar manner to the sale of the Admiral Gorshkov to India was tied to the sale of Mig 29Ks. The French CV Foch sold to Brazil for a 'giveaway price' of $15million whilst the A-4 skyhawks were bought for $74million, and I would expect the sale of an Invincible to be by far the smallest part of any such future deal, going for a token sum. This would be a wise move financially as the real money comes from the support contracts afterwards.