Is the probate process mandatory in WA state, is a copy of the Will valid

Is probate mandatory? No - voluntary, at least in the sense that there is no law requiring probate: There is no "Probate Police" who will come after you for not filing a probate upon a Decedent's death. Probate may be required practically, however, to access a Decedent's property, for example, a substantial bank or investment account, or to remove a Decedent's name from title to property, particularly real property, such as the Decedent's home.

Only a copy of a Will exists? RCW 11.20.070 provides a procedure for admitting a copy of a Will to probate.

An unrecorded Quitclaim Deed? A unrecorded Quitclaim Deed evidencing a lifetime gift & made by someone who has since died is likely void, as an improper Will substitute. Exception: If the Deed was held by a third party, out of the Decedent's control, & with instructions to record the Deed upon the Decedent's death.