Hi Joe
You and your mechanic are correct that if you listen to the engine and ensure that correct maintenance is always carried out, ahead of schedule then there is no reason to believe the car will not go on for years.
However, being equipped with a diesel of a large capacity and turbocharged, they do need running at high revs to keep them clean and free moving.
If you have no motorways in Malta then this could be an issue unless you can keep the revs high by manually selecting lower gears which would ensure the engine ran clean.
Problems which can be associated with insufficient engine revs are turbocharger variable vanes sticking in place due to carbon deposits, DPF blocking up and not able to regenerate, EGR valves sticking, carbon build up in intake system and increased engine wear and tear (sticking piston rings in worst case scenario, leading to lowered compression and fuel washdown, etc).
You seem to have plenty of technical knowledge Joe, which allows you to make personal choices and decisions and this in itself will give you an awareness of things not going in the right direction.....maybe the DPF delete is the way forward as the rules are different in Malta.
Will certainly get in touch next time I am over your way, haven't been there for quite some time though.
Regards, Trevor