It’s just going to depend on how good the healing magic in the setting is. Someone else was mentioning a Warcraft RP in one of the responses, and, granted I haven’t spent much time looking at that setting since Warcraft 3, but burns like that are pushing the limits of what someone can survive there.
On the other hand, I’ve got an Imperial Templar in Elder Scrolls Online who has half of his face, chest, and one of his arms, wrecked with burn scars. It’s one of the preset visual options. But, The Elder Scrolls is a setting where magic is so pervasive and effective, that not finishing someone off means there’s a real risk they’ll pop up later fully recovered, and in some cases (like the player characters in ESO) just killing them won’t do any good.
Depending on how potent magic is in your setting, you could potentially have a character with a partially exposed skull that’s unaffected, because magic is somehow keeping them alive. It’s all in your setting rules, and what the limits are for magic.
muffinsticks said: This seems like it went around the question… they asked how bad scarring can be without risking constant infection
Until you introduce magic into the equation, it’s a medical question… At that point, it’s “holes in the skin.” Once the skin recovers and seals it over, you should be mostly fine from future infections.
However, when you say, “but magic,” then it becomes a world building question, and it’s really going to depend on what your setting allows. I’m sorry if I didn’t make that clear in the initial post.