Since Bobby's full name was revealed to be Roberto Alejandro Martinez-Millan Luis Santiago, Jr. in "Study Muffin", it is possible that Mr. Santiago's full name is Roberto Alejandro Martinez-Millan Luis Santiago, Sr.
It is possible that Mr. Santiago is sick, as in "A Tale of Two Tables", it is mentioned that he had a hernia operation, and when Lynn Sr. asked Lori how it went, she answered "Um...okay, I guess".
He's not seen or mentioned in either "Shell Shock" or "The Loudest Mission: Relative Chaos", both of which Maria Santiago appears in. In fact, in both episodes, Maria appears to be raising Bobby and Ronnie Anne as a single parent--this is (sort of) confirmed by Maria herself in the latter episode, as she further implies that she's raising Bobby and Ronnie Anne as a single parent.
It is unknown as to what became of Mr. Santiago, but with this info he is either deceased, or he and Maria are divorced.
"There's Nothing Here!"
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