designed for it

Since the Enterprise is designed for travel at warp speed seperating from the warp field would not cause any damage. The Enterprise, at the time, was travelling at I believe Warp 9, once seperated, the saucer section would slowly lose there momentum till they were at sub-light speeds. The inertial dampeners would have protected the ship and the crew during and after seperation.

Design and emerging from warp fields.

Given that this manoeuvre is carried out using 24th century technology, and that Data states that it is theoretically possible to detach the saucer section at high warp velocity (although never tried, and there is no margin for error), I don't think this is really a nitpick. In any case the entire vessel routinely emerges from its own warp field every time it slows to sublight velocity with no ill effects.

that's not the problem!

The problem is that the saucer still made it to Farpoint by itself. I kinda doubt that the seperation took place close enought for the saucer to get to its destination on impulse drive.

I agree with the nitpick

Data saying it's theortically possible is just an easy way to not deal with the physics. If a warp engine protects the ship from the effects of traveling over the speed of light (or moving space around the ship as some say), then when they separate, the saucer would be subject to 'normal' physics and would most likely become infinitely heavy, infinitely slowed (time dilation), and/or destroyed. It shouldn't be able to bring them out of warp on it's own.

The answer is....

The answer is in Part 2 of the "Star Trek - The Collectors Edition" magazine, it states (and i quote) "The Enterprise's main warp nacelles are located on the vessel's drive section. The saucer module has its own engines which are capable of impulse and low warp speeds, thus allowing it to maintain considerable velocity after seperation". So, the saucer CAN travel at warp allowing it to stay ahead of the drive section and catch up with it later.

Technically, warp drive does not "push" a ship faster than light speed. Warp drive folds space, that is, it takes two disparate points in space and folds space over like a piece of cloth so the points are then next to each other. Technically, the ship doesn't move at all, space does, so if something like the saucer section fell out of the warp bubble presumably it would simply stop folding space beneath it and come to a rest in whatever part of space was around it at the time.

Warp Drive Operation

Warp drive actually is like Alcubierre drive, in that spacetime is being contracted in the front of the bubble and expanded in the rear of the bubble. Thus the ship is riding a sort of 3d wave of moving spacetime, and, because it is stationary relative to this local spacetime wave, it experiences none of the unwanted effects of ftl travel. Any portion of the ship leaving the warp bubble while it was still operational without the bubble's expansion/contraction being properly altered where the ship wanted to exit the bubble would be either crushed or ripped apart, depending on whether it went through the contracting part or the expanding part of the bubble. Also, subspace, as used in the series, and hyperspace are not the same thing.