That is what remains

It's something I thought about. If the three letters DAD had been said in Morse code instead of STAY, Cooper would not have left. But here's something to consider, or rather, something that Nolan himself places at the start. When Murph comes with Lander, who's starving for breakfast, Tom teases her by saying it's Murphy's Law.

Murphy's Law states that anything that can go wrong will go wrong. Just before the chase through the cornfield, Murph explains this to Cooper when their car develops a flat tire on the road.

However, Murphy's Law doesn't necessarily mean that bad things will occur; rather, it suggests that what is supposed to happen will happen. This is where the Grandfather Paradox enters the picture.

What would happen if a person traveled back in time and prevented their grandparents from meeting, effectively erasing the possibility of their own birth? But what’s the use of that thought experiment when these events have already occurred?

This ties into the film's exploration of time and causality. Along with the intervening "They" reference, Cooper tells TARS, while in the Tesseract, that "They" are future humans, meaning that ultimately, "They" are us. The implication is that they were left near Jupiter with a wormhole and communicated through gravity.

When you piece everything together, it suggests that whatever is supposed to occur will indeed occur. If time travel is developed in the future, it may not allow for altering events in the past but might enable a third-person perspective on them.

In some way, we may be able to intervene. But we can't avoid the central event. One last thought—it’s intriguing to consider that many of the things happening now could be orchestrated by people from the future. Or at least, if they have that capability. lol.