My Linkia Multiflora lived in my tank for just a little under a year. It has not died but, I did have to have my LFS hold it for me until my tanks are set back up.....I moved recently. I saw my Multiflora at the LFS today and it is still kicking in a larger tank.
The Linkia decided to drop an arm due to the fact of it's comfortability in my system. It felt that there was a good enough food source for it and good water quality and left an arm behind to grow a new starfish.
As far as the "fragging" of the arm went ~ I noticed the starfishes arm slowly starting to thin out at the base. After a little while it dropped the arm completely and just had four arms for a little bit. Then I finally saw the new arm generating four small nubs from it that are growing into full arms. My original Multiflora is regenerating the lost arm as well.
Keeping the Linkia Multiflora should go well for you as long as you are introducing the starfish into a mature tank.....your should be okay as it has been set up for a year now. The more live rock that you have the better. Acclimate for at least a 4-6 hour period and things should go well. Good luck.