PG's are only 15-20 years old. Quite "young" in PAF terms. By all accounts it still has a decent radar and turning ability, coupled with AIM-9L/M its almost BVR capable and can act as a decent gap filler and point defence aircraft. Also I know in PAF it's valued as a lead in trainer and DACM aircraft. The two Sqds we have are at based at Peshawar and Samunguli, so facing Iran and Afghanistan for routine air patrol duties. For that role they are more then enough as we do not expect armed confrontation in the air from these two in the future. I don't see the F-7PG leaving service for at least another 10 years.
Mirages are another story. Even the ROSE upgrade now is dated. PAF were very clever in obtaining a stock of relatively low hour airframes from all over the Middle East, France and Australia. Reserve is such we can just get any spare part we want from airframes in stock, no need to even go to manufacturer and where we do need to make something basic PAC has been doing for years. Essentially PAC could make a brand new Mirage from scratch if you asked them. This has made operating Mirage easy and cheap. Unlike issue India has with Jaguar which is same age. They have big fleet but no major spares reserve or spare air frames HAL has to produce every new part they need, also Jaguar is very under powered (they cancelled new engines over cost), Mirage was verlucky in having powerful ATAR engine. Not only had this enabled it to carry heavy loads like RAAD and H2/H4 but also provide enough surplus power for new equipment (Grifo radar, EW etc). This is why PAF love this plane.
Issue now is cost of upgrading this plane (replacing ATAR engine, AESA radar, ECM kit, new cockpit, HMD etc) is simply not worth it anymore. Add to that maintenece hours that increase for every flight hour due to age, training pilots to fly this plane. All of this is not worth it when we are churning out JF-17s at a relatively low cost and JF-17 has more capability. Only issue is we have simply so many Mirage Sqds that it will take at least another 5 years to fully replace all the fleet.