I missed a collectable during the prologue. Do I have to start over to get all of them?

A bit too late into the prologue did I notice that the little hexagons that float around indicate collectables that I can scan with the Focus. At that point I had already squeezed through a door which shut behind me, but remembered that there was at least one such indicator in the area before the door.

Do I have to start a new game to satisfy my completionist drive or will I be able to go back and fetch that collectable later?

Solution 1:

It is possible to revisit the ruins after the prologue and fetch any collectables that you might have overlooked. The ruins that the prologue takes place in are inside the Embrace so you can access them as soon as you start playing as adult Aloy (they are also marked on the map). Aloy is then able to pry open the door that locked you out as a child.

In fact, you might want to go back there, even if you did find all collectables during the prologue already...