I will try to keep this shorter than the actual story.

Beginning of December-Mom dies
Dad goes to west coast to be with son
End of December-son writes check for large sum from son and dad's (and mom's) account to keep safe as per mom's wishes. Leaving Dad with $60k to live on.
Dad/son get in arguement-Dad (age 90) gets in car and drives home to east coast.
Dad causes accident in Dakotas, police call son, police asked to hold him, they won't. Dad gets back to east coast.
Dad comes in closes accounts, takes check to begin with, ends up with exchanging checks a couple times and ends up taking all $60k in cash over course of a week or so. CTRs properly filed.
Son calls, wants to know if Dad closed accounts. Indicates Dad said he would put a "Hit out on son" for "stealing" money from him after mom died. Son concerned dad now has means to do this. Son according to Son, filed PPO on west coast.

Do I have a responsibility to file a SAR and what would be the reason?
As always, thanks.

I would not file a SAR. Presuming the father was entitled to the funds in all of the accounts which he closed, he engaged in no suspicious activity, and no SAR is warranted.

But if you believe the father to be a danger to himself or others, many states require that you report this to the appropriate Adult Protection Service authorities.

I cannot believe that the son would let a 90 year old man drive from the West Coast to the East Coast.

Don't get hung up on the age. My Dad is 94, and regularly drives from one end of the country to the other. He is a better driver than alot of others on the road. He has not had an accident in 40 years.

Maybe I'm off base here, but if you think this is serious, you may want to pick up the phone and call the police. I doubt anything goes down, but if someone gets shot or worse and you had prior knowledge, I don't think it will end well.

This is a tough situation. Maybe call like the Frog Lady says, Adult Protective Services and talk to them. They should be able to point your next steps.