It definitely is a hazard and probably not to code.
I would put back the piece you removed

It doesn't have to be exactly the same as it was before if you don't like the style (and if there isn't more of it further down the stairs), but you do need something there.

Please put something there. I had unfortunate fall, almost went down the stairs in similar situation. Looking up not down when hit unexpected drop off. Code required or not do replace with something to stop a fall.

Put it back, please.

Doesnt have to be the same. it could be be a pony wall or full wall if you prefer.

Perfectly fine. Whatwawawawaw

could happen?

You absolutely need to replace it. Either with the previous railing or another style. If you change it, I would get a matching handrail for the wall. Or as someone else responded, you could do a wall/pony wall but that would not be my preference and I believe would be more involved.

Yes it needs to be replaced with something maybe an interesting slat wall no railing at all there since it seems your wall railing comes right to the top of the stairs