In normal circumstances removing the battery won't stop the engine if the ignition is still on. This is because the alternator is, as said, is powering all electrical items, including it's own exciter circuit.
However this is all irrelevant with this particular turbo fault. The turbo compressor oil seal has failed. This has allowed engine oil to become atomised into the boosed air. Being a diesel, it will happily run on oil. Hot engine oil is combustible enough to run a diesel. So in this instance, the engine ran flat out in a self-sustaining manor. If there is no outside intervention, the engine will continue to run flat out until one of 3 things happen. Those are, bottom end or timing chain failure. Or all the fuel (oil) is used up. In the latter case, the engine may seize due to lack of oil (it's been burnt as a fuel). Or the fuel (oil) runs out and so the engine stops.