Can an ebstein's anomaly fatal?

Yes. Severe ebstein's anomaly may cause fetal loss and may lead to death in the first months of life. Abnormal heart rhythms can coexist with this and complicate managment. Most forms of ebstein's anomaly are less severe and many are asymptomatic.
Yes. The defect , an inferior displacement of the tricuspid valve & alteration in the size & shape of the right ventricle, can be severe enough to result in early death.