I like to use custom models for my maps but for some reason when I import a large model my Radiant freezes, then if I close it and open my map back up the map doesn't display in the 3D view and I cant move the 2D view around. Its weird because I can see the imported model in asset viewer and all looks fine. It seems Radiant cant handle the model and just keeps breaking any map I try to put it in. Perhaps the model has to many polys? Also is there a way to delete the model from my map in a file due to not being able to delete it in radiant? That would at least save my map cause it wont load or compile as of now. Any help regarding this issue would be of great help.

you can try to split that custom model in maya and then porting each part as a diferent model but it may end up crashing anyways because of the polys

and to delete models withou opening radiant do this:
 open your map with notepad++(or whatever you have) and search for your model's name, then just remove the commented line that says the entity number and the content inside the brackets{}

// entity 20
{
"classname" "actor_ally_rus_commissar_ppsh"
"model" "char_usa_marine_fullbody1"
"export" "1"
"origin" "592.0 -208.0 320.0"
}