How does a GRP motoryacht die?

Well, when is it "dead"? When it can no longer leave the dock under its own power? I think there are quite a few liveaboard boats that are not much more functional than being able to keep the water out.

There are also a lot of "dead" boats on the hard that get dragged from place to place by people thinking they can be "restored".

Is the Kalakala (not a GRP boat, but still...) "dead" yet? <grin>
Kalakala owner sues state and property owner, claiming anguish; he seeks more than $250M | Tacoma - The News Tribune

How long is a piece of string????? It depends on each yacht and what it needs and how much has been neglected and how much the finished yacht would be worth to it's perspective owner.....I've seen people spend 3x on a yacht restoring it, over buying a perfectly functioning sistership, just because it was their dad's or was theirs 30 years ago.......A small percentage of GRP yachts however have major fiberglass structural issues due to build quality, or water intrusion or whathaveyou that cannot be saved......

OK - I'll bite. It might end up costing the same, but it wouldn't be worth the same when done. It wouldn't have the new boat warranty (for whatever that's worth).

And some things are going to be a PITA that you're going to punt on.

New wiring? Lots of wires run through places that then became inaccessible. So you don't replace ALL the wiring, but there you are with "older" wiring with perhaps corroded terminals, owner-mods, and well, who knows.

Tanks? Are you doing to remove the tanks? Of course not, so you clean then...replace access hatches, fuel plumbing, etc. There are a variety of tanks and types, some with a service life which will be somewhat reduced. So, not "new".

Are you going to put a new gelcoat on the boat? You will never get the factory gelcoat. You can buff it, wax it, but...again...not "new".