I know OP you've said that you are trying to figure out how others handle FB "rejections" but the title of the post is asking if Facebook rejections are an etiquette issue so I'm going to address both.
I don't believe FB rejections are an etiquette issue because people use FB for various reasons. I don't have time to keep up with the newsfeed. For me it's strictly so people can reach me should they need to. I have several young ladies that I mentor who are on FB & their phone numbers change a lot, their emails too, but with FB they don't have to keep up w/ my contact info nor me their contact info. Send a FB message & we connect. That is the sole purpose of my account on FB.
2nd I have been rejected (& unfriended) & it hurt at first. However now that I've been on FB for 7 yrs, I just flat out don't care anymore.
One of my BFF's has never been on FB & we are closer than ever.
I hope you are getting some insight from all the collective wisdom of ehellions, because I remember at first it did sting to be rejected (or unfriend) but as time has gone by I realize different people use FB for different reasons. Like someone else said if FB went away tomorrow, well, for me, I'd miss it a little, but I wouldn't lose any sleep over it.
Also, I usually do not friend coworkers unless I know them very well, as in, we do social things outside of work, and even then, I have regretted friending co-workers many times. There's only 2 but they are very iffy friends, if friends at all. My mistake, & I will not unfriend them, but I regret friending them, as their true colors began to show later in our relationship.