How do you know when to replace tubular tires?
 

The answers i've received from the locals have been less than optimal - either wait until your tire flats or it comes off the wheel.

Is there anything more pro active I can do to know when to change the wheel before this happens? What do you guys do?

For reference I purchased Vittoria Pista Evo's. These will be race day race tires only.

My rule of thumb is that you can keep riding a tire until you flat on it, and stans won't fix it, or when you can see the threads in the tread. That said, I'm a poor junior, so I tend to stretch some equipment out longer than may be totally advisable.

A properly glued tire should never come off!

Some flats can't be foreseen, but keep a close eye on nicks in the rubber and when if the tire starts squaring further than you feel comfortable replace... I just ride till it flats or squares badly.

You'll want to replace a lightweight race tire like the EVO Pista before it flats. Keep a close eye on the (very thin) tread and when you start to see some nicks that expose the carcass, change it. This can happen pretty quickly to this tire on a concrete track.

Following up on my very first day on the track with the Vittoria Pista EVO CS. Within 50m (30 seconds) of getting onto the warmup circle of our track I had ripped off a .25in circle of the black rubber.

That was the most expensive and time consuming lesson i've learned so far. Spent a week gluing them on properly, only to have it destroyed within 30 seconds of first use.