Legal Question in Real Estate Law in California

Escrow papers are usually signed only at the end of the transaction, at the closing. So of course an escrow is legal if the buyer didn't sign. You are barking up the wrong tree looking at the escrow. The binding documents are the purchase/sale/deposit agreement and related documents. The escrow is just a place to deposit the things to be exchanged (money, deeds, reconveyances of mortgages, etc.) to make sure that the transfer of title does not occur until funds are on hand to pay everyone who is supposed to get paid and any new lender will get their mortgage recorded. The escrow is merely a vehicle for performance of the obligations under the contract between the buyer and seller. If the buyer disappears the issue is breach of contract not a problem with the escrow.

I'm not sure what you mean by the escrow papers. Most CAR purchase and sale forms are also joint escrow instructions. Both parties have to sign the escrow instructions to open an escrow. During escrow, amendments that are material to the transaction must be signed by both parties. But documents are also deposited into escrow, such as deeds, deeds of trust, etc. are signed by the party conveying, and not the other party.

An escrow can be opened by only one party. At that point, it is "legal" and "valid" but not anywhere near ready to close. It cannot be closed (satisfactorily, at least) until all necessary parties have deposited their instructions, documents, money, etc.