Clutches are covered by warranties,but only if they fail due to a faulty part and not if they wear out.
Clutch pedal wear isn't a sign that the clutch is on it's way out to be honest,and as long as it feels OK and doesn't slip,it should be OK.
I guess this car is from a Renault dealer,so it is more than the garages reputation is worth to sell a car that has been clocked,and if you have researched the cars past,you have to believe it is genuine.If the car has been serviced by Renault,then you should be able to trace the cars history by asking for a service print out.This will give you details on what has been done and at what mileage.
As for the part exchange deal,the dealer probably has someone lined up for your car and wants to seal the deal.Either that,or the car your looking at has been on the forecourt for sometime(not neccessariy for any untoward reason) and he wants to move it on.Car sales are pretty slow at the moment,so he probably just wants his commission!
If you are in any doubt about the car,don't buy it!.There are 1000's of used cars out there,so if your not 100% happy with this one,go somewhere else.As I said,sales are slow,so you could negotiate your way to a bargain.
Good luck and let us know how you get on.