Jambo:
Bear with my story for a moment, because I think I'll have some good advice for you in a minute:
I have been in my industry for 30 years, and am approaching the point where I am going to pack it in. I have an obligation to see through a 'bail out' temporary assignment I took on to help another dept, so it's been good meeting the new leadership team, getting them acquainted, but also odd because I am purposefully distancing myself from future assignments and responsibilities -- something I have never done. I finally took both of the new leaders aside and explained my general intent. I had already (stupidly?) sat with my HR person and told them the same. Both HR and the new management expressed surprise and I think some disbelief that I am really going to just up and leave -- HR wanted me to 'come talk for a follow-up in a couple of months'.
The perfect random situation would be if we were bought up by some yet-to-be known of company, and they put me on the list to get RIF'ed, but I don't think that is going to happen, and I sure don't intend to wait for it -- I never want to get to what one of the former mil guys called ROAD -- I hated seeing those useless guys taking up space when I was in the military. So my point is that mentally, I am already planning to be gone, but attitudinally, I don't hate my old job, or even my current assignment, or the new team, or anything. I'd like to add value while I remain, but I do not want anyone to give me something I will need to leave as unfinished business or leave anyone in the lurch.
So, at long last, here is my advice for you -- even though we are getting different pressures (mine think I am 'bluffing', your treat you like you are already gone) I think our approach needs to be the same:
Take the weeks you have to get out of the office, and do some "Management By Walking Around" and some networking, that you may (if you are like me) wish you had always had more time for. You can help those in the trenches by listening, and you can help those that will remain by using your (I assume) former heft and gravitas to freely speak your mind on any observations /issues you see. In the last couple of weeks, I have felt that I am seeing clearer, and advising more plainly than I ever have. So far from being ROAD, I feel I am the opposite -- getting a 10,000 ft view, and able to translate that (with my past experience) into some bullet 'watch for this, check on that') type advice for the new crew, with the admonition that they need to assess for themselves, too. Oddly, we have been an organization in crisis, and I think the turn is going to come, and that is good, but I do not have the heart to stay with it. That is what is freaking out HR -- much of what I thought needed to go or be done is in the works, and much of what used to bug me is getting at least noticed if not addressed... but I just don't see myself being a part of the next era.
So take your days, be the elder statesman, make the rounds of colleagues, slap some shoulders, freshen up your contacts in your Rolodex for Christmas cards and such, and let it go. Don't insist on being in the thick of things and decisions, float above it and at best give some general advice and thoughts if you are asked.
Good luck!