Theories are not "proven" as much as evidence is collected in favor of a particular theory. It's a question of what exactly does the new evidence question - here if you believed that mangroves had a more ancient origin - the new evidence validates your theory and refutes the mainstream view. If you believed that all life on earth arose spontaneously around 6000 years ago this has no bearing on your belief.
In science, you don't risk hell-fire if you happen to be wrong on something. Scientific theories are meant to be modified if new evidence happens to prove the old theories wrong. What many creationists wrongly believe is that any flaw in any aspect of evolutionary biology invalidates the entire field - just as perphaps among fundamentalists any error or flaw in Scripture invalidates the entire thing.
Conjectures are not considered theories until they are well established. I can't name off the top of my head an established theory that has been proven wrong.
More commonly, a theory is shown to have limited applicability, and is replaced by a theory covering a greater range of observations.