We don't know. It's up to each nation under the Baha'i Commonwealth what they will do is my understanding and the rights of the minority will be respected. I was concerned about this and wrote the Universal House of Justice. Here is my query and their reply:
Is there any definitive guidance on what we will do when the Baha’is become a majority in a country? Will the national assembly take over? Or will we form a new government by other means. I am worried about shutting people out of the administration of a government. I am afraid we will cause bad feelings. Could we have a different law for Baha’is and other people so as to not impose Baha’i law on others?
Mr. Duane Dawson
Dear Bahá’í Friend,
The Universal House of Justice has received your email message of 12 June 2018, seeking guidance about the nature of the administration of a country when the majority of its population will have accepted the Faith and how in that circumstance minorities would be treated. We have been asked to convey the following and regret the delay in our response. It is not possible to describe with particularity how the governance of a country might be affected when the majority of its people accept the Faith. However, any change will be by democratic means and not by force. The writings of our Faith make it clear that under a Bahá’í system the rights of minorities must always be respected and upheld. Shoghi Effendi has enunciated this principle:
Unlike the nations and peoples of the earth, be they of the East or of the West, democratic or authoritarian, communist or capitalist, whether belonging to the Old World or the New, who either ignore, trample upon, or extirpate, the racial, religious, or political minorities within the sphere of their jurisdiction, every organized community enlisted under the banner of Bahá’u’lláh should feel it to be its first and inescapable obligation to nurture, encourage, and safeguard every minority belonging to any faith, race, class, or nation within it. (The Advent of Divine Justice (Wilmette: Bahá’í Publishing Trust, 2006, 2015 printing), p. 53) With loving Bahá’í greetings, Department of the Secretariat