Escort engines can go several hundred thousand miles - and pistons fragmenting has not been a failure that I can recall. (Not that I have read every posting!) But detonation can destroy a piston in 5 minutes (though usually it takes longer torture before they fail), and a dropped valve seat - if someone kept driving it - would certainly ruin one or more pistons. It smashes the piston top enough that there is no clearance between the wrist pin and the pin bores in the piston. Then the piston will begin to melt as it starts 'siezing' itself to the wrist pin. This is a source of more heat/stress than anything except detonation. In such a case, either the piston would fragment, or the con rod would break.
Its possible the piston had a flaw - but that also seems rare. I have rebuilt 3 2nd gen. Escort engines. They all needed piston rings (oil control rings at least), the ring grooves cleaned out, and the head milled. The highest mileage one had 200k miles on it. I had the cylinders honed only because I took it to the machine shop to get the water jacket cleaned out. In all 3 engines (all over 100k miles) the original pistons went back in. I probably didnt need the new crank/rod bearings, but heck - they were not expensive. New seals of course. On one of them I replaced the core plugs in the block.
Since your Escort is a 3rd gen, I believe it has a knock sensor. If that failed (or its connector came loose), the pistons could have begun to melt just driving from Denver up to the passes at 10,000 ft.
I would also recommend you check each con rod for still being 'unbent'. One of my Escorts had already dropped an inlet valve seat when I bought it. I may rebuild that engine some day; but to put the car back on the road, I got an engine from a JY car - and rebuilt it. The engine with the dropped valve seat had two pistons that were no longer easy to rotate on the wrist pin - and had battered tops, and piston rings that were jammed in the smashed ring grooves. I wouldnt have trusted the con rods either.
Sorry about the need to give you bad news.