My problem with killing off Nobara right there, is that for someone who is part of the main characters, she didnt had enough development or momentum yet compared to Yuji and Megumi, to go out just like that. Unlike Nanami who was more of a side character and got his dead just a couple of chapters before fullfilling his role in the story. Nobaras "dead" right after would feel more like killing for the sake of killing and shock.
You say it was a key factor for Yuji to know who he was and all that. But id say Nanamis death and Sukuna doing the japanese equivalent of 9/11 already served that purpose. Throwing off Nobara like that right after would feel cheap, especially for a main character, is even worse when Yuji keeps remembering Nanami and his last words everytime he gets the chance afterwards, but nothing about Nobara.
For me the best outcome would be for that encounter with Mahito to serve has a landmark for her character, this time scarred for life (this should be a big deal considering how she always cared about her appareance) and quite possibly with a new resolve and approach in life.
I would still respect Geges decision if he ends up killing her tho. But that wont change my mind in seeing it as a waste.