Sankharas, once eliminated. Do they have a chance of coming back?
There are ten fetters eliminated in Vipassana meditation. Elimination does not occur before you reach the Sothapanna(stream enterer) state. Until then, fetters are only subdued. Once a fetter is eliminated, it's gone for good. Refer to the table below to know the fetters eliminated at each stage of the path.

Yes, if you stop doing vipassana short of attaining Sothapanna, your mind can fall back to an ordinary corrupted state again.