Through a legal process, a guardian maybe appointed to exercise the legal rights for an incapacitated person, who the court finds is at significant risk of harm based of a "demonstrated inability to adequately manage property or financial affairs" or "demonstrated inability to adequately provide for nutrition, health, housing or physical safety." (See Revised Code of Washington (RCW) 11.88.010.)
Washington state law does not require a probate case to be filed following death, regardless of whether the individual died with or without a Will (i.e. testate or intestate, respectively). Probate in Washington is entirely discretionary, meaning if a probate case is filed, it is because someone wants it to be filed, NOT because the law requires it.
Washington law does require that any last Will of a Washington resident be filed promptly following death (within 40 days of death at most). If a Washington resident died with a Will, then the Will is required to be filed with the Clerk’s Office of the Superior Court of the resident's county at death (e.g., Thurston County Superior Court) regardless of whether or not the estate will be probated.