To be fair, you can safely go cold-turkey with Vyvanse - but withdrawal symptoms start after 2-3 days and can last up to a week. I'd describe my withdrawal experience as feeling utterly bored and being uninterested in doing anything, even passively watching the trashiest of shows on TV. I imagine that's what clinical depression (without actually feeling sad) is like.
Weaning-off it is far more preferable.