PLEASE HELP -

I have a Dracaena Palm that I have had for 25 years. I think it may be 40years old. I know it sounds ridiculous but it was given to me by my grandmother and I am extremely sentimental about it. I moved a year ago and it hasn't been doing good since......although the plant has been moved several times in the past. Originally I had three stocks in the pot but two have already died. The plant has always done great. It has gotten so big (almost 8') and has even flowered each year. But since my move this is what it looks like. It gets afternoon indirect sun, watered (tap water) when it gets almost dry, and miracle grow every three weeks or so. Its the same as what I have done for the last 25 years. However, I did realize it was too close to a wall heater that I only had turned on for two days and shut it off immediately. Now the top of the tree trunk is turning black and get squishy to the touch. Is there any saving it?? Should I cut off the hanging portion or will it kill the whole tree? I am desperate because the tree is so sentimental.