take care of yourself, is usually a term of endearment. in other words i hope to see you again. now, it can be in concern. did the earlier conversation include you having some difficulty or medical issue? it still leads back to an endearment.
freind of mine was sick recently. on the way out, i said, "take care of yourself", meaning i hope to see you again....
in other words, if you were heading out the door, would your rather hear, f off and die!, or take care of yourself ?
unless the person is a real jerk, it means, they hope to see you again....