If the foot is attached the nem may have a chance . if a nem is handled to much they tend to close up (stressed out),
the problem is we tend to over feed a nem . "were like hey" that's neat lets feed it again
a small piece of shrimp 1/4 inch in size is enough, if you do this try to do it only 1 time every other month ,
nems can survive with good lighting and anything they can get from the water column .
there's no real reason to feed a nem ,
I had a green long tentacle nem I fed it often , little did I know I was over feeding it , the poor nem died from my mistake . like I said above a nem really can get by with just strong lighting and what it can catch in the water column ,
with that said you can still feed your nem just don't over feed , a 1/4 inch piece of shrimp every other month will keep your nem happy ,
I would give him a few months to recover . before attempting this again or just let him be , remember every-time you feed your tank food particles spread through out the tank . the nem will catch this food in the water column.
but if you notice the flesh starting to deteriorate That is a sign that it's dyeing off . that is when I would remove it from the tank ,