With the absence of bylaws, is it appropriate to open the membership to all present and willing to join and vote? - B.D., Dec. 5, 1999
A:
Your situation is quite unusual.
You're without governing documents (bylaws, rules of order), but have been functioning for some time without them.
Apparently your chairman is elected, but a replacement can be appointed by the resigned chairman.
Quite unusual, indeed.
In many ways, your organization is like one that is just starting "from scratch."
Without governing documents, you have no specification of membership, so it would be the same as that of a mass meeting: all invited persons who attend.
The purpose of these meetings is to decide on a purpose for the organization, then start the organization process.
The details are too numerous for this discussion.
Your best first steps would be to (1) hire a registered parliamentarian to assist your organization in organization, and(2) become familiar with RONR Sections 52 (Mass Meeting) and 53 (Organizing a Society).
As to the election, since you have no specification of officers (found in the bylaws), there is no office to fill.
Get thee to a parliamentarian, quick!
Quite unusual, indeed.