This is a trickier decision for me than the one about Darrell Bevell for the following reasons:
First, because it's the front office's decision to acquire or not acquire certain players, not position coaches. They have let numerous offensive line veterans leave (Unger, Carpenter, Okung, Giacomini, Sweezy, etc.) without paying for sufficient replacements. That is why the Seahawks were dead last in offensive line spending the last few years.
Second, because Tom Cable is a highly respected offensive line coach throughout the NFL who has always been committed to a strong running game. I have viewed him as a counterweight against Bevell's finesse tendencies that has often times helped to keep the offense afloat during Bevell's worst moments of play calling.
Third, I am not sure even the best offensive line coaches in league history would be able to accomplish much better with the likes of Rees Odiahmbo, Luke Joeckel, Oday Aboushi, Alvin Bailey, Bradley Sowell, Paul McQuiston, Patrick Lewis, Drew Nowak (former DT), Garry Gilliam (former TE), or Kristjan Sokoli (former DT).
People are quick to assume that the offensive line coach is leading the charge in the front office to acquire these cheaper players instead of high-priced veterans. I can't assume that because that's not how the delegation of authority typically works within an NFL organization. The scouts, GM, and head coach typically play a greater role in player acquisition than the position coaches themselves. Coaches "coaching" is how it normally works.
Cable's greatest sin has been his inability to campaign for more and better resources along the offensive line. That very well could be his downfall this off-season.