The fact is they did extend the lifespan of the AL-31 according to this article. Now if they can extend the lifespan of the AL-31, there's no reason the newer design WS-10A will not at least match that lifespan. In fact more likely the WS-10A will exceed it. The problem they were, at one time, having was production issues which has nothing to do with the design of the engine. One of the reasons, imo, they made the decision of not retrofitting the J-10 / older flankers is that it's cheaper and less hassle to continue using the AL-31F engines. The WS-10A still needs to be modified to a version with a different gearbox position for the J-10, not to mention the aft fuselage of the J-10 / older flankers (including for example the engine's holding brackets) would need to be modified to fit the newer engine.