Yahoo's explanation of what is ACTUALLY going to happen to Yahoo Groups is unclear.
Why won't Yahoo offer some real-time chat or even email support in order to EXACTLY understand what is going to be changing in Yahoo Groups. I have managed a group for over 15 years, and I can read, but it is NOT clear what exactly is happening, nor any specific helpful information on what to do at this point.
What stays is you having the ability to send an email and have it distributed to all the members of the group
Everything else - attachments, digests, archive, files, polls - will be gone.
I think you'd better start looking for an alternative, such as groups.io or groupspaces.com