If you block it off it will stay clean and continue operating as it should (although no exhaust gasses will pass through it). This will prevent it failing again as the soot builds up, requiring another replacement.
The EGR valve is designed to let in a controlled amount of exhaust gas at part-throttle steady cruising rpms. It reduces nitrous emissions by about 10%. They also cause no end of bother, as they let in soot from the unburned diesel back into the air intake, this mixes with the oil mist that seeps past the turbo seals or from the crankcase breather, and together they form a sticky tar which slowly builds up inside your inlet manifold. In your inlet manifold there are 4 swirl valves, one for each cylinder, they act almost like little throttle butterflies, narrowing the aperture into the cylinder to help speed up air flow into it at low rpms, increasing efficiency. These go wide open at high rpms and close fully on shutdown to prevent engine judder. The soot/oil mix settles on the spindles of these valves and causes them to stick, which also triggers an error - the fix at a garage would be a new inlet manifold if, which is a cambelt-off job to fit. This hasn't happened loads of times yet, but already we are seeing more and more, it is the same with these engines in Fiats and Vauxhalls too. The Vauxhalls that are coming up big mileages seem to be the worst effected. But the engine is the same. Do a Google search for 'swirl valves', you will be shocked!
This is not just an Alfa problem, BMW had a similar problem a few years ago, but worse, as the swirl valves were breaking off, getting chomped by the inlet valves, sometimes making their way into the cylinders and scoring the bores, writing off the engine. Sometimes they'd pass harmlessly through the engine but smash through the turbo on the way out.. Either way, expensive..
To blank off, replace the gasket where the EGR pipe exits the exhaust system with a thin sheet of steel. Some people blank off the EGR at the intake end, this will prevent soot getting back into the intake but not sure whether this will prevent it building back up in the EGR pipe.
Hope this helps