1) What does Islamic ruling of syed sistani mean when he says obligatory precaution?

2) I was following doing taqlid of marja when he was alive and then I change my marja to different marja when he was still alive. Now after he's death can I go back and follow my past marja even though he is not alive anymore or no?

3) When can a person follow another marja's verdict not her regular marja? What is requirement for following another marja verdict?

4) Can a person follow a deceased marja's verdict or no?

1- Obligatory precaution means you must follow the ruling unless there is another Marja’ who allows it, so you can follow that other Marja’ who allows it

2- Many scholars stare you cannot go back to his Taqleed since he passed away

3- If your current Marja’ says it’s obligatory precaution, or it has been proven to you that another Marja’ is more knowledgeable in the ruling, then you can follow him in that ruling

4- Most scholars say no (unless you followed him when he was alive and you stay following him).