I am not ready to call OD a fumbler and I doubt if Kubiak is either. If I recall correctly, his fumbles came in high profile situations so they are more easily remembered. If anyone has his career stats compared to some other TE's, I would be interested in seeing them. I remember that at least one of his fumbles came when he was hit really hard from behind while he was fighting for extra yards. Maybe when he is in that situation again, he can remind himself that he may be about to be decapitated.
If the coaches are not satisfied with OD, I doubt that Dreesson replaces him. More likely, they draft someone next year to compete with him.