Im sorry for your losses... But I wouldnt give up if i were you. It is possible to get a healthy one. I have one in my tank that has been in there for over 8 months. Couple of things to consider are:
1. Was it healthy when you got it? When i finally bought mine, it was in a tank with 30 other Blue Linkias that had been at the LFS
for 3 weeks. I kept going back to the store 2-3 times a week to check on it.
2. Acclimation? I drip acclimated mine for 3 hours before adding it to my tank. (i see you did a 7 hour drip, maybe the LFS
didnt do as well and it was suffering from SG
3. Handling? Never Ever touch one with your bare hands. Your skin touching the linkia can contaminate it, causing it to deteriorate (please don't ask me why...) Whenever i need to handle it, i stick my hand inside of a glad bag and use it like a sterile glove.
4. Air? Direct exposure to air is a nono. Make sure that the amount of time that the linkia is out of the water is minimal to 0.0%. Like a sponge, direct contact with the air can kill it.
I hope that helps.