If the mast got bent or dented you'll need replacement. And getting one with a boat attached might be easier than getting a solo one. If that's the case, tough luck and good luck hunting for a new DS. The rest of this post assume that the main damage is to the hull.
Fiberglass is infinitely repairable - except that nobody has infinite budget for materials or unlimited time. Those two tend to be the main limiting factors. A third one is making sure that the repairs don't add too much weight.
There are three main objectives in restoring major damage.
- Restore watertight integrity
- Restore or even increase strength (stiffness)
- Restore the original hull shape and fairness
I'm ignoring the obvious fourth one, restoring the outward appearance, for the moment, because it's something that you might well need to do anyway for a boat that hadn't been damaged structurally.
With fiberglass, getting the repair watertight is usually not an issue. Fiberglass that's been weakened could still be watertight, but in order to get strength back you might need to replace it or double it with new laminate. Every time you take out a large section of the existing hull, you'll be faced with the problem of how to get the new laminate to follow the correct shape, especially in areas that have compound curves. If you leave weakened (soft) laminate in place but double it with new laminate, you're adding weight. Luckily, the DS is rather heavy, so a few pounds here or there will not dramatically change the way it sails.
Since what you have is a DS1, the hull is accessible from inside and outside (except where the floatation tank, seat benches are). That makes a repair that much more feasible. The nice wooden parts though, are not as repairable. You may need to fashion replacements should the coamings or thwarts be broken, rotted or both.
Much depends, therefore, on what the damage is. If falling beams have pulverized large sections of the hull, especially those with compound curves, you'd be attempting to rebuild the hull shape for those section. Unlike the original builders, you'd end up trying to lay up laminate without the benefit of a mold.
If, instead, we are talking about one or more "puncture wounds" or even a longer gash or rip in the fiberglass, that would be more encouraging. In those cases, new laminate would only have to bridge shorter stretches and getting a fair hull shape afterwards isn't as difficult. Tricky spots would be damage to the flotation tanks and seats, as they are enclosed volumes. The most difficult areas might be those were the hull meets deck, seats or bulkhead.
If a falling beam "broke off" a piece of the boat, you may only have one "seam" to fix to put it back on, but then you'd have the challenge of accurately positioning the part and the rest of the hull so that you don't cement it in the wrong position.
I suspect the economics are such that any attempt to hire out this work is doomed. Used boats are just so much cheaper. I can understand your willingness to invest a bit more sweat equity into a particular boat for sentimental reasons, so make a thorough survey of the damage and we'll help you come up with an estimate of what time you'd need to invest.
Unless your DS is in a state where reassembling it would require the same skills that archeologists use in putting together Greek urns, you might find that the fiberglass work takes only as much, or less, effort than the later "surface" treatment, i.e. painting. (And if you have gotten another fixer boat instead, you might needed to paint that also).
In fact, that would be my personal cut-off. If the structural work can be carried out with about the same effort (or less) than it would take to fair and paint the hull inside and out. If it takes much longer, you are better off going sailing.
Final note: do you have access to a heated garage to work in for a few months? If not, I'd forget about this project. Epoxy resins really like to be cozy when they cure. And if you can't work on this over the winter, you'll tech your boys how to spend their summers doing fiberglass work, instead of being on the water...