First, I have always appreciated Tony Clark as far back as when I was a Tiger fan and he was drafted by Detroit the 2nd pick over-all in the '90 draft (just after Chipper Jones) and was very elated when the Dbacks initially signed him. True, his penchant for being clutch and all the attributes he provided (especially his leadership skills) will be missed, however, he's not the only main leader. There's still Kirk Gibson (who to me still should our manager, but that's obviously another issue all together) who even was even among Clark's mentor when he ascended through the Tigers organization.
I also agree w/an assertion that some columnist made awhile back (if the Dbacks were indeed to lose Clark) that the younger players take lead by themselves... Eric Byrnes has some leadership skills (except when he made that pathetic remarks during the NLCS that seemed to rally the Rockies more so) and then there's obviously Orlando Hudson, Chad Tracy, and to a lesser extent Chris Snyder.
Again, it's a must that the players become more accountable by themselves and disseminate what they learned through Clark and have an individual like Gibson who will ensure that they never lose sight of all their objectives.