No effect unless McClendon is forced to sell shares to cover the loans. This occurred back in 2008 when McClendon faced a margin call and had to sell 94% of his shares. The stock's price stabilized at around $13.50 before rebounding over time, but there was some pretty severe short term damage.
If McClendon is that leveraged, and he can't liquidate his interest in the wells, guess what? He will have to liquidate shares again.
If McClendon is forced to sell shares, that'll be GREAT. We'll be able to pick up more on the cheap. This company is selling at .76x book value and a forward p/e of 6.7x. With its solid revenues, prime assets, and natural gas bottoming, it's a takeover target.