The Mandal wanted Ambedkar to join its reform struggle rather than exit Hinduism

Evidence

In fact, we thought you would give us a lead in the destruction of the evil of [the] caste system, especially when you have studied the subject so thoroughly, and strengthen our hands by bringing about a revolution and making yourself as a nucleus in the gigantic effort, but [a] declaration of the nature made by you, when repeated, loses its power, and becomes a hackneyed term. Under the circumstances, I would request you to consider the whole matter and make your address more effective by saying that you would be glad to take a leading part in the destruction of the caste system if the Hindus are willing to work in right earnest towards that end, even if they had to forsake their kith and kin and the religious notions. In case you do so, I am sanguine that you would find a ready response from the Punjab in such an endeavour. — Ambedkar, B R, Annihilation of Caste_ The Annotated…, 780