You can have your pick of rumors this morning about why COO Tom Rutledge suddenly decided to leave — and what it means for Cablevision’s future. Maybe he had a falling out with Charles and Jim Dolan, who control the No. 7 cable operator (including Verizon and AT&T in the pack). Maybe Rutledge got a better offer to run Charter. Maybe the Dolans decided to try again to take Cablevision private — or to sell the company, logically to Time Warner Cable considering how many adjoining systems the companies have in the New York area. But since nobody really knows, investors are left to fear that the departure of one of the industry’s most respected operators means there’s trouble ahead: Cablevision shares opened down 13%. If that holds, then it would shave about $506M from the company’s market value and take the stock to its lowest point in more than two years. Miller Tabak analyst David Joyce lowered his stock recommendation to “hold” from “buy” — and lowered his short-term price target to $15 from $22 –saying that the news “puts a question mark over the 4Q11 results.” He says that the downgrade could be short-lived if the Dolans try to take the company private or sell. ISI Group also downgraded Cablevision to “hold.” Brean Murray Carret analyst Todd Mitchell, who already has a “hold” recommendation, says that he believes Rutledge’s departure is due to “some sort of falling out with the Dolans.” He was paid $28M in 2010, has three years left on his contract, and had already rejected an offer to run DirecTV. If the Dolans don’t sell, the analyst says, then “Cablevision is likely to see further deterioration in its fundamentals.” Wells Fargo’s Marci Ryvicker, who also has a “hold” recommendation, takes a similar view noting that Rutledge probably forfeited about $2.8M of his 2010 bonus and $15M in retirement benefits by leaving on the first day when he wouldn’t also be required to repay Cablevision for his stock awards. Although there’s a lot of speculation that Rutledge might move to Charter, which is looking for a new CEO, she notes that Rutledge’s contract includes a one-year non-compete clause. If he isn’t leaving for another job, then Ryvicker says that the news may indicate that “the Dolans may be taking more control of the core cable operations.”