Engines are amazing things, Renee. Neglected, they can fall to bits in a surprisingly short space of time. But treat them properly with the correct preventative maintenance and you’d be surprised how far they’ll go before they wear out.
What you haven’t told me is whether your vehicle is diesel or petrol powered. That said, both the diesel and petrol engines fitted to this model Pajero are well regarded in the trade and capable of going the distance if, as you claim, the servicing has been by the book. Over the distance you’ve quoted, I’d expect the diesel to have needed possibly a new turbocharger and definitely new fuel-injectors, while the petrol V6 can cover this distance without any major work.
But while the engine might, indeed, have lots of life left in it, what about all the other components? The brake rotors, shock absorbers, transmission and many other intrinsic parts of the vehicle wear out, too. So, just because the engine is fit and healthy, doesn’t mean the rest of the car will be so tip-top and ready for another 300,000km.