Is funny, most stage managers would never think of quitting a show, or calling in sick, or asking for time off - until you get on a long running gig, and especially a long running commercial gig, when you are three years into a show (or longer) you realize the show indeed goes on, and you can leave - for a day, a week, or forever. Part of being a good stage manager means making sure the show can transition and continue when you leave for a day, a week or forever.
I am in my second year at the same theatre and had to finally step up to the plate and ask for a weekend of a show off. I have a wedding the last weekend of an unconfirmed extension. I was so extremely nervous to even broach the subject, but my husband insisted that if I never asked, I would be upset with myself. I spoke to the stage manager informally first, asking what she thought, and she said to go for it and email the production manager. When I did, I got a positive response, and they will have someone fill in for me the last few shows. Then in a crazy twist, the SM's daughter finally nailed down a date for her wedding- the same weekend. So the stage management team will be replaced for the weekend.
I moved far from home, as did my siblings, so we all rarely get together at the same time. As much as I love my job, I can tell you that looking forward to an event with my entire family (something that rarely happens once a year if at all) is a real highlight.
Now I have put in a lot of time and good work to feel comfortable asking for time off, but at least now that I've asked once, I won't be so fearful the next time something really important comes up.