Would you say they are past the point of potentially being talked out of it...once kinda recently I was having a bad anxiety attack and thought of suicide and told my mom and said I should go to the hospital but she talked to me and I was able to calm down enough to where I felt safe...so sometimes people just need to be listened to.

If you don't feel you are capable of handling it perhaps suggest they call a crisis line or try to get some help if they are like in contact with you and talking to you and seem reasonable....otherwise like the other poster said if they have blatantly said they are going to do it and have a plan then calling 911 would probably be best.