Just got an oil change on my 2012 mazda3/skyactiv where they found my air filter was missing - it was supposed to be replaced at my last oil change 7000 mi ago but they never actually put the new one in. The box that holds it was not latched, and was pretty clean inside. They flushed the engine with oil, which came out a little darker. Did this do major damage to my engine? Any suggestions on what to do next?

 

Unfortunately you won't know if any damage has been done until something goes wrong. The air filter is the last line of defense before air can make its way into the valves and pistons. Since you haven't noticed any engine issues, nothing big made its way in. Small particles could have gotten in and may have scratched to walls of the pistons but at this point it hasn't effected anything, and there isn't anything you can do about it either.

Just get a filter in, like yesterday.