I don't know a whole lot about Fords, but in my experience with GM vehicles, the water pumps tend to start weeping a little bit of coolant when they are wearing out, gradually developing into a steadier and more serious leak until finally the coolant system will barely hold pressure. This cycle usually takes quite a bot of time, giving you lots of warning before the pump fails entirely.
If you aren't seeing puddles of coolant under your vehicle and don't have the time to get it fixed, your pump is probably at the earliest stages of failing. I [i]myself[/i] would probably go ahead and take a 600 mile trip. I'd also take a jug or two of coolant along, maybe even a new water and the tools to install it, and just monitor the situation. I'd be pretty confident about making the round trip without incident.
If you aren't mechanically inclined and don't really know how to keep an eye on it, best to get if fixed beforehand, however.