Top 10, yes. In TOs they were top 5 I believe, but not in Total D. Nonetheless, teams change and injuries happen. Even with your proposed D, I don't believe they would recapture the magic from the first 11 weeks in 2011.
Delmas specifically has huge injury potential. Jackson, Young, and Tully might never return to that same level of play due to a variety of factors including age, injuries, and opponents learning how to play better against the vanilla D the Lions use, mostly because the DL is not as dominant as many of us would like to believe and without that dominance the D's weaknesses in back 7 quickly get exposed.
Every year the team is different from the prior year. Is it possible for Mayhew to find a formula that will work in 2013, yes. Will it take more than getting Werner and having LoJack, Young, and Tully back to their best level, absolutely. They are still exposed at CB, S, and OLB even with those 4 guys at their best plus Houston and Delmas playing at their best for the entire season.
Still, even with that they will not likely be top 5. Nor do we necessarily need the D to be top 5. top 15 will likely result in being a playoff contender and top 10 would likely mean they have a legit shot at the NFC CG. And remember, during that 11 week stretch they only played 2 teams that went to the playoffs in 2011 and lost both, so even when the D was humming along at arguably their best level, the team needed to be considerably better to have any legit shot at a playoff win. Notice how the Niners improved since then? Notice how the Lions did not??? That is due in no small part to coaching and the FO, which is what many of us have issue with currently because the Lions had a chance to get to that level. They were earning respect, the atmosphere was positive, and they let it all slip away. Now they are back in rebuilding mode again due to the FO and coaches not having the ability to get the right guys in place to sustain what was working well, let alone improve.