Gray Matter is essential to Walt's story though; None of this would have happened without them. However I don't think he's going back just to get them, really I'm not sure we'll even see them again in the finale, possibly but I wouldn't bet on it. I think that he had for a moment given up after feeling that he'd completely lost his family and any hope of helping them but then his ego which has driven him all along was attacked and this pushed him to continue with his previous plans whether he could help his family or not just pure revenge. I expect to see him go after the nazis and if he does go after gray matter I think he's more likely to try and ruin the company (with bad press maybe) rather than kill one of them. The writing has never been flawless in breaking bad but I don't think this episode is one to attack it with.