Oooh, this is something I know a little about. At university we were tasked with building software for estimating the usable area of a runway given its configuration and obstacles.

Runways have 3-4 different defined areas, each with different properties and usable in different ways. For example, the grass at the sides is important for safety, must be cleared a certain distance back, must not rise above a certain level above the tarmac, etc, and all those rules are distinct from the rules that apply to the concrete at the ends of the runway, distinct from the rules regarding surrounding buildings and trees, and so on. The area managed as a runway can extend kilometers out on every side.

Now, if you have a plane break down at one end, or a support vehicle crash on the grass or something, you don't actually have to put the runway out of action, but you do have to re-declare the usable distance, and that's based on the location, size, and importantly height of the obstacle. You then need to plot the angle of landing/takeoff based on that height, accounting for the segment of the runway it's in, and the given runway's pre-approved angle (varies by city/terrain).

It was a fascinating project and a good example of how problems are often so much more complex and nuanced than they initially appear.

Overweight landings are a thing and it's very, very rare for the airplane to break apart or even be damaged when performing them: https://www.boeing.com/commercial/aeromagazine/articles/qtr_...

Generally, the displaced threshold is not because of the load of touching down, but because of clearance of obstacles. When landing, where you are aiming to land, and a standard glideslope, puts you over obstacles at a certain height. In some cases if you landed on the very end of he the runway, that would cause you to collide with (or have too low a margin of safety) over obstacles before the runway. The displaced threshold moves the glideslope further forward, allowing for better clearance over obstacles.

Source: Advisory Circular 150/5300-13B Airport Design, 3.5.3 (https://www.faa.gov/documentLibrary/media/Advisory_Circular/...)

  When it is impractical to locate a threshold at the beginning of the runway, it may be
  necessary to apply a displaced threshold. A displaced threshold reduces runway length
  available for landings in one direction. The portion of the runway prior to the displaced
  threshold typically remains available for takeoffs. Depending on the circumstances
  surrounding the displacement, operations from the opposite runway end may or may not
  be affected. Refer to Appendix H for related information on declared distances.
  Generally, a runway threshold displacement provides:
  1. A means for obtaining additional RSA prior to the threshold.
  2. A means for obtaining additional ROFA prior to the threshold.
  3. A means for locating the RPZ to mitigate incompatible land uses.
  4. A means for obstacle clearance prior to the threshold.
  5. Increased arrival capacity with certain parallel runway approach procedures. See
  FAA Order 7110.308, Simultaneous Dependent Approaches to Closely Spaced
  Parallel Runways

Glossary:

  RSA: Runway Safety Area
  ROFA: Runway Object Free Area
  RPZ: Runway Protection Zone

Note that all of the given reasons are for clearance of obstacles or various other mandatory safety areas based on clearance from taxiways or other runway traffic, not for durability of the runway.

I don't think the airplane is going to break up, just that it would need inspection and perhaps repair if touching down over weight.

Blancolirio covers this: https://www.youtube.com/watch?v=4D2Kj0t4t9s