We had a couple of hot days, and in spite of me seeing a parent shading the chicks, perhaps one succumbed to the sudden heat. The other seems fine. I saw it gazing around skywards, looking for a parent returning with food and comfort.
The weather is cooler now, and the surviving chick is back in the wooden box.
Well, that is a bit sad. I doubt anyone will interfere and remove the dead chick. It is as nature happens. Falcons have been nesting in the same spot for many years, although I read somewhere that they didn't for a couple of years after a falcon fed illegally poisoned pigeon meat to the chicks. The surviving chick will get more food and probably thrive.