The cause of death is known. That’s not the same as the Coroner’s verdict. The Coroner doesn’t look at the cause of death, he/she looks at why it occurred and what category it fits into. In a criminal investigation where there is a possible court case this won’t conclude until any criminal proceedings have occurred. The fact that Russia won’t extradite doesn’t alter this as it may not be the case in the future.Dawn Sturgess has still not been given a coroner's inquest, meaning her family still have no legal/medical cause of death.
However you’ve already been told this on many occasions so I don’t expect this to sink into your thick skull any time soon.