Most are already working on other projects. For example, the people who are experts in the inner workings of Git and Mercurial are part of the Cloud Source Repositories project (https://cloud.google.com/tools/cloud-repositories/docs/).
I work at Google on Google Code, so I am happy to clarify a few things.
# What will happen between August 2015 and January 2016
The vast majority of projects will be "read-only", but everything will pretty much work the same. The frontend will look the same. You can brows issues, downloads, wikis the same. You can even sync code using a DVCS client like svn, git, or hg.
i.e. all the data that was there right now will stay there until January.
Projects will still be able to be exported to GitHub via code.google.com/export-to-github. In addition, project administrators can still use Google Takeout to get a JSON dump of their projects issues.
There are a few projects that will stay read-write for a few months, for example /p/chromium and /p/android. These projects will keep doing their issue tracking on Google Code until a replace issue tracker is ready.
If a project needs some administrative action, such as deleting a project or setting up a "project moved" URL you can contact [email protected] and somebody (most likely me) will twiddle the bits on your project.
Important note: All links to code.google.com will continue to work as normal.
# Coming soon: The Google Code Archive!
Obviously deleting ~a decades worth of open-source project data and breaking millions of links would be a very bad thing. Nobody on the Google Code team wants that to happen, so we are working to ensure that doesn't happen.
Tomorrow we will hopefully launch "The Google Code Archive" which is a slimmed down frontend for Google Code that renders an archive of project data, served from App Engine and Google Cloud Storage.
This Archive site will continue to host public (and only public) Google Code project data years into the future.
While it is in beta, the Google Code Archive will use a different URL scheme than current Google Code projects. Later this year, we will have the Google Code Archive frontend replace URLs to the old project hosting frontend. So urls to old Google Code projects will continue to work, but be hosted from a new website. (But you should be able to switch to the old one if need be via URL parameter.)
# What will happen after January 2016
After January 2016, we will turn down the old frontend and only serve data from the Google Code Archive.
The data that won't be preserved is private data. Things like issues labeled with Restrict-View-* (which only project admins, committers, etc. can view). Or projects that are marked as "Members Only". I haven't analyzed the exact numbers here, but this doesn't make an appreciable amount of the data on Google Code.
The big difference in January however is that we won't have the DVCS frontends running any more. So you will not be able to sync project source code using svn, git, or hg. Another outcome of this is that we won't be serving raw repo contents.
Hopefully that clears things up. Happy to answer questions.