I heard that Bob DeMoor had wanted to at least finish off 'Tintin and Alph-Art' after Herge's death, but Moulinsart turned him down...
If you wonder why, I suggest you read a couple of Barelli, Bob de Moor's own series. It's, hm, interesting, but it gives an idea why so many people pretended not to hear anything when Bob de Moor was suggesting to continue Tintin.
Graphically, it's quite close to Herge (strangely, I find them closer to Jo Jack & Jocko than to Tintin). In fact, it's half-way between Herge and EP Jacobs, which is why De Moor's talent was called for Blake & Mortimer after Jacob's death. But when it comes to the story, dialogues, and visual jokes (oops he slipped and fell haha, ooh they collided and fell too lolz), it's a good reminder that what made Tintin great isn't something that could be just passed forward to an apprentice, or something that the studio's coworkers would be necessarily able to emulate. A person who worked in the studios have a good feeling of the visual style of Tintin, and maybe the characters mentality and attitudes, but crafting a Tintin story, with all the simple-looking-yet-complex humour and plot, demands quite a unique talent.
One great thing about the serious "pirate Tintins" (Rodier's, etc) is that they illustrate well, through their cataclysmic failures, how demanding a real Tintin story is. Reading a few of them, as well (unfortunately) as a few Barelli, makes me happy that the "no new official tintin" policy is still upheld.