It is possible. Take every form of government issued ID, like the DL, but other forms that corroborate it. He should get to the airport extra early, and even more because it is a holiday. If he does not yet have a ticket, I would suggest not flying from LAX but choosing an airport like BUR or LGB, SNA, ONT--even if that means a connection, he will likely have a simpler and faster experience at a smaller airport. He (and you) should also look up the information on the TSA site if possible. And have him make appts for a passport and a REAL ID and print copies. It could help that he shows due diligence? It is the officer's discretion, but they simply deem him safe to fly and so far people are allowed.

Also, I am very sorry for his--and your--loss. How sad. No wonder that was not his first priority afterwards.