Google-groups – Polls in Google group

As far as I can understand what your problems are...

• You want to know how long attachments are kept in a Google Group?

As long as Google doesn't warn you that the file will be deleted, I think they will last as long as the message they are attached to. Just like in Gmail, attachments will not get lost as long as you don't delete the message they were send with.

• You created a groups with a name, deleted it and want to create a new one with the same name?

Many services block usernames once they are used. Most probably Google Groups does that too, so you will never be able to use that username again if you deleted the group. The reason why they do this is to avoid the circumstance in which some people keep mailing to a deleted group and that someone else that recreated the group will see their messages.

The following, as the OP describe, might work without notifying anyone else.

1. Create a Calendar event
2. Add the group to the invitation list
3. Expand the group
4. Save the event
5. Choose not to notify the guests
6. Open the event
7. Click Email the guests
8. Copy the email addresses
9. Delete the event
10. Choose not to notify the guests