A Warlock has chosen the Pact of the Tome feature. At level 5 the invocation chosen is Book of Ancient Secrets. The Warlock has now two 1st level spells that have the ritual tag written into the Book of Shadows. Along the way the Warlock inscribes two more rituals into the book by finding them in other spellbooks, and spending gold as described in the invocation. The Warlock now has four (4) rituals in the Book of Shadows.
The Warlock levels up to level 6 and decides to change invocations, replacing Book of Ancient Secrets with another invocation.
What happens to the rituals inscribed in the Book of Shadows?
Will they still be kept in the Book of Shadows, or does something happen to them as a result of replacing Book of Ancient Secrets with another invocation?