>>538047526
1. The player character wouldn't know the non-character's father is still alive. Are you metagaming?
2. The non-character would accept being replaced by a more competent spellcaster. The non-character can't even decide the value of his father's life in Act 3. The non-character is a glorified hireling.
3. I've never said that the narrative assumes a rigid party size of four. But it does assume a relatively small party. Temporary allies are completely acceptable - in fact, the screenshot above is a good example of that. Having Minthara or Jaheira or Aylin join you doesn't really break immersion - having a ten-strong party does. Why doesn't your party in BG2 gather all the available companions? It makes no sense to leave valuable allies behind! Clearly, the narrative assumes that you have a small army of twenty trusted companions by the time you face Irenicus.