The other guy I could have seen developing decently into the hold up role at striker is Jimmy Tulloch - although maybe his frame suggests something more of a target man. In either regard, he's gone too.
I wouldn't be so worried about the lack of a guy who can receive the ball and wait for support, but employing Mattocks at one of the striker spots seems to necessitate having a guy who's strong with the ball at his feet in the other spot. Darren has good pace, some flair, good finishing, and the all important "nose for goal," but absent good support play, those things become virtually useless.
I don't wanna seem all doom and gloom, and we should still roll past the Western Michigans of the world, but idk idk