I think the recent reporting has shone an important light on the extremes of adoption and how awful some of those experiences are for adoptive families, which is a good thing.
Adoption legally creates a situation where it “as if” the child was born to your family, and in that sense it’s a forever relationship. Even when adoption breaks down that child/young adult has changed your life irrevocably so that too is forever.
In terms of violence and aggression I think for all parents there’s a point where behaviour can become so extreme and dangerous that parents decide they can no longer accommodate the child at home, that they aren’t able to support them practically. In those situations with birth parents social workers will work very hard to keep the family together for many reasons, not least because it’s very hard for all concerned to take a child into care. It’s exactly the same for adoptive families - social workers will work very hard to keep the family together because they are your child first and foremost.
The gap though is lack of supports and specialist service that can come around the family together work with trauma and adoption. Instead of dedicated adoption teams, families are referred into statutory child protection teams who have a legislative framework based on the responsibilities of parents to care for and raise their children. Taking a child into care generally means there has been a failure in parenting fundamentally, however in adoption there are obvious complicating factors that are often just not considered and that services have no easy way of dealing with. Funding for all services is such that for birth or adoptive families there’s little support until they are in crisis - by which I mean there’s a significant danger to the child or adult, because there’s no money for early intervention.
The question of how you communicate to your child they are no longer welcome in your home is a hard one, but that would be the same for a birth child who had a reasonable expectation they could live with you in adulthood. No one tells a birth child they have a forever family, but the hope and intention is that they would. I guess though the “forever” part is dependent on that being a safe living environment for everyone,