You are slotted to attend either a Saturday or a Sunday op, not both, depending on your squad. For example, Jackal 1-2 (my current squad) runs Sunday, but my availability Sunday is horrible. I informed everyone in my medical and combat CoC that there may be times where I either bug out early or don't show up for Sunday operations due to a legitimate issue. If you have a real excuse, send a PM up your chain and nothing bad happens, it's just an excused absence. Of course, a ton of excused absences also raise questions, but if it's all honest-to-god, then it's all green. Unexcused is if you do not notify anyone, or as you said "AWOL". "AWOL" is more when the unit doesn't know you are here at all. From my understanding, few unexcused absences start with a Time in Grade reset, followed by a demotion, followed by a boot. A ton of excused may earn you a space in the Reserves platoon but I don't think they grant the boot for legit missing stuff. We all have lives, and we have active duty here as well, so everyone understands that at any given time, something could come down and next thing you know, we gotta be gone (a good example is i thought i had a PT test at 0300 on a Monday, so i'd miss a Sunday op, but ended up being a hoax).
TL;DR -- can't attend for a legit reason? Send a PM to your first line leader