A replacement should be fairly quick since CATIC/PAC can make at least 20+ planes a year.
Training attrition is common to all air forces including those of far larger air forces such as the USAF. Planes are less important. The object is to give the pilots the minimum flying hours necessary to maintain competence. Most air forces want their pilots to have at least 150-300 hours of flying time on combat aircraft each year. So over a 10 year career of a fighter pilot at average of 2000 hours of combat flying experience is accumulated. Since the JF-17 was inducted around 2010 it is likely that most JF-17 pilots would have had at least 1000 hours on this type. There is wear and tear on the aircraft which is why training flights are also a great test of the competence of the maintenance crew to keep the air craft flying. Valuable maintenance and engineering data is gathered and a crash itself ( with the pilot surviving) is a great way to learn improve the aircraft. Of course the latter point only holds true if the aircraft is designed and manufactured by the country operating it. A foreign manufacturer is unlikely to share any details of engineering and design faults and would likely blame the pilot.
Training is essential:
Having pilots sitting in their quarters and the planes parked in the hangars waiting for a war to happen is not a desired policy. Some underfunded and weak air forces are forced to do that with disastrous results. The planes and pilots were preserved and achieved nothing.
Example:The air force of a particular South Asian nation (equipped with J-7s ) were battling an internal ethnic insurgency. The insurgents had developed a rudimentary air strike capability flying converted twin seat propeller utility aircraft. Because of a lack of training the underfunded air force though otherwise adequately equipped were unable to stop a devastating attacks by the insurgent air force on both their international airport, and key airbases. The damage inflicted by these light planes was very substantial destroying several military and passenger aircraft, maintenance hangars, communications buildings passenger terminals,and killing over 200 personnel. The insurgents pilots were superbly trained and made the best use of their aircraft. They even got away safely after the first two raids, expertly maneuvering their planes and flying low to avoid detection. This South Asian nation ultimately had to request another friendly South Asian nation to loan it pilots to fly its F-7/J-7s ( since that nation was flying F-7/J-7s also), and hunt down the insurgent planes. This was done and the J-7s flown by foreign pilots neutralized the insurgent air force both by ground strikes and in the air.