There's two things that are pretty important to convey here:
1 - We'll be in close contact with you as any changes come, and will work to minimize pain and negative impact.
That's not to say that there won't be any, but we're going to do our best to not let this turn out like a home makeover reality show where you come home to a bunch of Nascar fan art and beer kegs, unless you really happen to like Nascar and beer.
What's most important to us is that you come out of this feeling heard, considered and as accommodated as we can possibly manage.
2 - There's room in the side bar to keep customizations
Jon and I both mentioned this in a few places that aren't likely to turn up in searching because of context, but our plan is to keep the existing functionality while putting it in a place where it finally looks less bolted-on and more deliberate.
With the addition of the fully responsive design, we finally have the ability to control how pages collapse in different sizes, which should stop the image from becoming pain point in navigation for anyone using the full site on an odd display.
What I'm not sure of is what might change for size / aspect requirements, but we'll communicate that to you well in advance. I can't imagine much else about the mechanics of it changing, but like I said, communication from us is going to be a pretty big deal as the time comes.
If anyone has questions please feel free to leave a comment, ask a follow up question here or on MSE, or contact us directly if that's easier for you.
tl:dr; -- You're keeping it, but it might be a bumpy few days while we get everything settled, and there might be some changes to the mechanics of how the feature works and the requirements for images that will appear in the new spot. We'll let you know well in advance, and give you any help you need to transition.