Stovebolt was not started to solve Title issues or give legal advice. So all these type questions should be in the greasy spoon. Now my too sense.
First, I don't know the Texas MVD laws. As advised, talk to them in person and tell the whole story. If you find a worker who does not have a headache or stomach ache or not getting a divorce that day. You may get help or an idea of what it will take.
The truck will show on the records as belonging to the widow. No one else. IF IF IF the MVD can look it up by a VIN you have or a license plate number it will show she owns is. If Texas takes a Bill of Sale for a truck that is still on record as widow owned, I will be surprised.
If they don't find it or can't find it because you don't have an identifying number. then see what they say. If the Bill of Sale identifies the truck using a number of some kind, VIN or motor number AND IT IS NOTARIZED, that may help.
I myself would not buy it unless the widow goes to the CA DMV, pays for a duplicate title. signs the title as seller, with notary, if required, and mails it to your friend. Be aware to tell her she is not asking to register it. That will cost big late fees. She just wants a $4 duplicate title. She gives the VIN and her ID and they give her one. If her relatives get involved, which they will, your friend is screwed and the sheriff will come pick it up.
If you "buy" it, you may not be buying it. Your friend will fade in time the, lady will pass and you will have a mess....maybe. It's not the best thing to get involved in. Your friend was VERY negligent. VERY. Let it go or get it for almost nothing. I have had friends get vehicles seized and hauled away for this stuff. Deemed a stolen vehicle or sold improperly by a person with diminished cognitive abilities.
No bonded title, no salvage title, no bill of sale for me. I don't think CA requires a notary on the title. If she has no one to help her. Go there and help her.