I think any decent DC is going to be fine if he has a healthy Donald and Ramsey. Not to say that Staley didn't do "anything" but the GB game and season in general showed that it was a lot more about Donald disrupting things, allowing others to benefit and Ramsey taking away their top target. We saw all year that the Rams could have trouble getting off the field, making a stand or getting a crucial stop.
I have no complaints about the D as it carried the team for most of the year but let's be honest, this wasn't your typical #1 D. It had great stats but wasn't really akin to the '76 Steelers, '85 Bears, '00 Ravens, etc. Which is to say, I think we can maintain the very good defense we had, especially if a good DC is brought in. I just don't think Staley re-invented the wheel or caught the league off guard with some unique or new approach. I trust Snead/McVay to bring in someone who will work. Phillips was a good hire and did well enough. Staley was a HR. No need to think they can't find the next DC.