Injectors

But at 200k you're probably on borrowed time if you only have OE filtration.
As mentioned though, if you don't have symptoms of leaking or high return rates you're still in good shape.

I'll assume his Duramax was an LB7 made form 2001 to 2004.5. The eighth VIN digit will be a 1. These had lots of injector problems. GM eventually issued an extended warranty on the injectors.
I wouldn't relate his failure to your completely different engine.

On high pressure common rails it will also dilute your oil thin enough to grenade your motor.

Just watch for white smoke at idle, or immediately after a warm start. Caused by an injector dribbling fuel into a cylinder (not seating properly). A leaking injector can also burn the piston, so if you suspect leaking, pull them all and have them tested.

Extended cranking time can be caused by low batteries, but also because the injector return rate is too high and it cannot generate enough rail pressure to fire an injector. The computer requires more than 5k psi before it will start pulsing injectors. If fuel is being bled off by the injector, it will take longer cranking time to generate pressure, if it is achieved at all.

If you don't have white smoke, long cranking times, or shaking/loping at idle, don't worry about it.

My relative's work Dodge broke down at 590,000 miles doing light freight work. It needed a head gasket and related kit. All other parts including injectors were within spec. Cross hatching still visible in the cylinders.

Without better filtering, your Cummins could be in need of injectors at any time now. It's not uncommon for them to need replacement b and between 175 and 275K. Some go many times that. It all depends on how clean the fuel was over the years and that breaks down to plain luck.
Bosch wanted Dodge/Cummins to use 2~3 micron filtering but they haven't improved it unit recently. The best thing a Cummins owner can do is to add this filtering with something like a Glacier Diesel kit.
I would add the filtering now but be ready to replace injectors sometime in the future.

First generation Duramax, if that's what he has have injectors that are know to fracture. They do not make new bodies anymore and all replacement injectors use old good bodies which is a good thing because it means they weren't ones that failed earlier.