Sometimes anemones can deflate, puke their guts out, shrivel up into nothing or float off and disappear for days. If its been in the tank for more than a month it's always better to let it be unless it's obviously dead. Removing it and placing in a bucket might protect your tank but it will not help the anemone, more likely it will do the opposite. I would try to put it back into the tank in a low flow area and watch it closely. Until it is actually dead it's not going to hurt your tank.