Adhesives made for plastic models generally work in two slightly different ways. The thin liquids (applied by brush) are simply solvents; they dissolve the surface of the plastic. When the adjoining pieces are squeezed together the softened plastic intermingles; the solvent then evaporates. So there's no question of longevity as far as the adhesive itself is concerned. It's gone within a few minutes. If the plastic parts have been squished together sufficiently, the joint should last indefinitely.
The thicker adhesives (generally in tubes, though I think some of the bottled varieties may work this way too) also dissolve the surface of the plastic, but don't evaporate. Instead, the cement sort of "soaks into" the adjoining parts and hardens into a thin (we hope) permanent membrane between them.
I don't know of any reliable scientific data on the longevity of such adhesives. (I question whether such data exists; the stuff hasn't been around long enough.) I can, however, provide a little anecdotal evidence.
I have a model of H.M.S. Bounty, based on the Revell kit, that I built in the late 1970s. I modified it extensively (seven of the kit parts survived), using basswood, boxwood, degame wood, brass, copper, nickel-chromium wire, sheet styrene, silk thread, britannia metal, and probably some other materials that I don't remember. The adhesives I used on it included Revell tube-type cement (no longer available), Testor's liquid cement, 5-minute epoxy, cyano-acrylate "super glue" (which was just appearing in the stores at that time), Franklin Titebond (wood-to-wood joints only), Elmer's Glue-All, and DuPont contact cement (for the copper sheathing). The model looks as good as it did 25 years ago (thanks largely to its plexiglas case), and not a single one of the glue joints has shown any sign of coming loose.
The only adhesive I avoid is lead-based solder. Lead, as you probably know, is one of the least stable substances around. It used to be a common material for castings supplied in ship model kits, but nowadays it's virtually disappeared. It used to be hard to find lead-free solder, but recent government safety regulations have led the manufacturers to sell lots of it. Hardware stores, home centers, and Radio Shacks all stock solder that works well for model building.
Modern adhesives, properly used, seem to be remarkably durable. I don't think there's much to worry about on that score.
Regarding belaying pins - I imagine what you're talking about is the pinrail (the horizontal piece that holds the pins themselves). Pinrails are, indeed, an Achilles heel of sailing ship modeling. I suggest two tricks. One - drill two or three horizontal holes through the ship's bulwark and into the back of the pinrail. Then shove a piece of wire, with a drop of "superglue" on its end, into the hole and cut the wire off flush. Two - hide a small, square strip of basswood or styrene under the pinrail, at the joint with the bulwark. Even a 1/16" square strip will substantially increase the surface area for the adhesive, and the support will be invisible from an normal viewing angle.
Hope this helps.