That isn't really the whole story regarding our history. Yes, some of that perhaps happened. But many others departed willingly and on good terms. Actually the Millerites fragmented and dispersed after the Great disappointment. Some returned to their old churches, some banded together to form other groups. And even those who remained a part of the Millerites that became known as Advent believers continued to interact with their own churches and other churches. But the Millerites didn't as a whole simply regroup and reorganize. As for "no choice but to form another organization", that is also not really the case either. You do realize it was nearly 20 years after the Great Disappointment of the Millerites that a growing segment of Advent believers finally got together as the Adventist denomination and actually formed a new organization in 1863. But even then there actually was very strong resistence to forming a new and separate denominational organization.
You also mistakenly make it sound like that this group of rejects and outcasts from other denominations started all over as a new denomination completely fresh in discovering Truth without any reference to their old doctrines and beliefs. The truth is that they all came bringing those, some of which were not in dispute, others which were restudied and refined. And a few new beliefs and doctrines emerged among Adventists. But much of what we have, including our worship forms, structure, and doctrines are common to various other denominations as a result. As has been said many times before, we have far more in common than we have that is distinctly different.
And even after the Adventist denomination was organized, the early Adventists continued to interact with other denominations, meeting with them and preaching in those churches. Ellen White herself was a much sought after speaker by other denominations and often preached in their services on Sunday. I just read an acount from one of her letters from 1891 where she was telling of a large non-Adventist meeting that she and a number of other Adventist leaders were attending. In her letter she made positve reference to a well known, at the time, woman preacher from another denomination that was speaking. And EGW was encouraging others to come to that meeting.
I think EGW was more ecumenically minded than many assume. In addition to the above, she encourages Adventists to work "shoulder to shoulder" with those of other churches in activities for the common good, such as the temperance movement and other welfare ministries. She also encouraged our pastors to fellowship with and pray with the pastors of other churches. She also spoke of pastors of other denominations positively, referring to them as fellow shepherds of the flock of Christian believers. She also encouraged coming together with other beleivers on "common ground" which seems to be a basic ecumenical idea.