I can't see how the dealer is justifying stripping the engine, if the adblue was added in place of diesel, the engine would have stopped because the adblue thinned the fuel to the point it would not ignite, ergo the engine stops,it's not like he's put the adblue in the oil filler hole and it's swimming around the oilways causing bearing damage, inside the cylinders there is water vapour produced during normal running, nothing the engine can't handle. The fuel filter would have retained most of the water.
Drain the tank, change the filter and it should be fine.