A Cohen cannot be metamay to a relative that is not “whole” certainly a missing arm or leg would be included but where do we draw the line? What about a missing eye? what about an internal organ like appendix or womb or tonsils? what about missing teeth?
Internal organs are also considered to be a lack which renders the body incomplete, and hence a kohen would not be metamay.
However, this is only if the detraction from the body takes place after death.
Shulchan Aruch Y:D 379:9. Shu”t Minchas Yitzchak 5:9:21, Shevet Halvi 3:161:4, Tzitz Eliezer 9:48.