Hi Omar
My wife has an Audi A3 with cylinder deactivation as did my previous car, a Skoda Octavia 1.5 TSI - the revs don't drop when switching to 2 cylinder mode as the engine is still running a 4-stroke cycle, just with 2 cylinders "empty". In fact, apart from a message on the dash, you rarely notice it has switched to running on 2 cylinders. A very impressive engine (well the 1.4 one in the Audi is, the 1.5 equivalent was a nightmare, but that's a whole different story....)
All the best
Glen