Well as @MominHaq said , PIA should first recover itself form its financial crisis before planning to replace any aircraft.
For the sake of the topic PIA should replace the 747's with new 747-400 or 747-800 , there is a since of pride and prestige for PIA in owning a four engines aircraft (747) .
Other option maybe , they can use their 777 on long haul flights and get new 737-800 NG or A320-21 aircraft's for short to medium haul flights .
A380 in my opinion will not work for PIA as that aircraft is designed for long haul and hub to hub travel , and as far as i know PIA is losing its ground ( routes/destinations) to other airlines,.......... as far as i know there are only 2 main hubs for PIA outside Pakistan and they are Manchester and JFK New York , A380 will only be profitable for PIA in Hajj season.
Now the Livery of PIA what i liked ( my opinion )
1 The 80's livery with Green tail and Gold Cheat lines
2 The 2004 Provisional tail livery
3 The 1999 Green Pashmina Tail livery
Please do correct me if i am wrong .
Fahd.