Awais bhai first of all why engine is going to die only after 125k km? Check this from some expert mechanic because blow is not only due to pistons / rings, but may be due to bad injection timing or faulty vavle stems or seals. Secondly, if u want to change, then 5afe/4afe will cost 60k~70k in rawalpindi (mithu khan Ehata), a friend of mine swap that. This price was without gear box. your resale value will go up after swap bcoz very few people like diesels.
By the way ur ride is owsum. I also own a 2.0D 2001 model.