After looking at your file, I see that there is a lot of unnecessary geometry, meaning vertices and edges stretching across large planar areas which, in themselves, define no surface curvature. If efficiency is the goal, you will want to avoid accumulating large numbers of vertices and edges on flat surfaces. Remember that the purpose of the vertices and edges is to define shape. If there's no shape, there shouldn't be any vertices or edges either.
I believe this efficiency consideration is important to point out because, the very spot where you are struggling is precisely a place where you have a lot of edges on the "mane" side of your Knight model. Precisely because of all those edges, you are now in the difficult position of trying to find out how you can fill your hole without creating ngons. Perhaps it didn't seem obvious at first, but if you can't get rid of an ngon any other way, there is always the possibility of actually REMOVING geometry to solve the problem. Sometimes this is the best option.
Here's a cut down version of your file. You may not like the shape, but it should be pretty close to the shape you had. But it has a lot fewer polys where there was no shape defined. And so getting rid of the hole was easy. You may be able to apply a shrinkwrap modifier to get some of the lost shape back. Remember that not every visual contour needs to be modeled. Most of the ribbed texturing on the knight's mane will be able to be faked with texturing.