Throughout human history and to this day, when certain religions survive and flourished, it is due in large part to the patronage and support of the government in existence then, or some powerful person of the period with all its resources available to be used when and where necessary.
Undesirable as it may be, but where extremists and militants existed in a religion, it acts as a deterrent to prevent other faiths from trying to convert the followers of that faith. When religions have Commandments, and when the breaking of such Commandments would entail immediate punishment, it ensure that followers stick to their particular faith. The Buddhists in the north eastern and other regions of Arunachal Pradesh do not have all these means at their disposals. At best, living conditions are likely to be rudimental.
To keep Christians Evangelists from carrying out further conversion of Buddhists in that region, there is certainly a need for the Indian Government to send someone influential, who is sympathetic to the Buddhists to put a check on all these forced conversion by the Evangelists presently in this area.
Most importantly, charitable Buddhist organizations with the resources, and also committed, experienced Buddhists in social works or with some life skills should come forward and offer their services in Arunachal Pradesh.
If no outside Buddhists and their organizations are prepare to come forward and serve as volunteers like the Christian Evangelists do, than it is inevitable that eventually the whole regions will be Christian dominated.