You know what, I think we should abandon the 2 weeks of paid vacation.... At the rate we're going, nobody will use up all their time year-by-year, and some things (medical/family issues) are beyond our control and we shouldn't be penalized for that, or debate it.
Instead, how about the person on vacation is strictly required to give notification prior to their absence (which hasn't been much of a problem, anyway), and if we're not notified ahead of time... well, we can take it from there.