Then we'll have to wait and see. The Heart alone seems a bit... lame, I guess. I think there's a bit more to it.
In one of the latest purpose, Earl did say that Order is necessary - I for one will agree that having church searching for heart is not so bad as Earl can easily snatch it. And perhaps maybe the exorcists can be able to get near the heart safely or suppress it power so Earl wouldn't be in harm. OR Earl wants Order to obtain the heart, which could bring their self-destruct because of lack of knowledge what the heart really is.
Cross and Allen can't stop them from doing anything; they're not powerful enough. At best, they'll split off and form a third group. However, I doubt the Order is quite that foolish. If their actions will bring about their downfall, it will be deliberate on their part. Why... who knows yet.
I believe it would be as cool as Order was really on path of self-destruction and Earl knows they actions are completely futile - but of course Cross, Allen and others will learn about it before Order makes mistake and stop them from making such.