No it's not 100% doomed.

Its 99.99% doomed.
no its not

Never purchase one that has any white spot on it.
i would not either unless very cheap
One little spot, and it's a gonner.
no its not just very stressed
I bought 2 linckia star about 3 weeks ago. One is doing fine but
the arm tips of the other one seem to be disintegrating slowly. I know
Linckia star are hard to keep and I read that they often lose the arms
and die. Are the symptoms of mine similar? Is there a chance that it
gets better or is it 100% dommed. I am in a position where I want to
give it all the chances it needs to get better but I do not want it to
suffer if it will die for certain.

if the tank parms are good meybe you just need to feed it i put mine in a
small floating fish breading tank with white bait as food. when he has eaten
enogh he climbs out back in to the rest of tank