Are there plans to sunset Fireworks in the next year or two? If so, what is the timing, and what is the recommended replacement?
I have not heard of any "sunset" plan but the replacement you choose will be affected by the type of work you have been doing in Fireworks (prototyping, UI/UX, etc.).
In cade you issued it, here is the official statement from Adobe on their blog:
This recent article suggests some general alternatives such as Sketch, Macaw and Anetype.
What Does The Future Hold For Adobe Fireworks?
If you need prototyping, I enjoy using Adobe Muse for prototyping web sites
Other possible replacements for Fireworks include:
Affinity Designer (Apple Design Award winner).
Xara Designer Pro about near as you'll get to Fireworks:
Evolve UI (Open Source) by Tribaloid
Gravit (currently in Beta and available by invitation)
If you choose to continue to use Fireworks today, you will be interested in Fireworks extension resource sites such as these:
Hope this is useful for you. :-)