the diamond can chip or cleave if hit hard or just the right way, but it's not anything to lose sleep over. the color will remain the same. If you have an IF or FL stone, better to leave in the safe deposit box so it doesn't get scratched or chipped.
Settings degrade. Becuase I sew, I am particularly hard on plain solitaire settings. Most newly engaged don't realize that settings look out of style, crap, bent, and worn out in a few years. (oh, i will have this for the rest of my life...!" uhhh, no you won't, hunney.
so don't be surprised if she wants to change out the setting in 5-10 years.
Symmetry should be constant provided the diamond doesn''t break, polish can downgrade due to chips and nicks etc, but a diamond can be repolished with minimal loss of weight in some instances.