During a round of Temple Trekking I had an encounter with ghasts. I was properly equipped, but the problem was, one of them attacked the NPC I was escorting. It never attacked me, so I couldn't attack it back... The NPC was rather weak, and even though it tried to fight back, ghast pwnt him despite the fact I fed him a lot of food... Is there a way to have a ghast switch to me, so my pouch makes it attackable for me? Or is this situation hopeless?

in that case your best hope is to use the escape option, but I'm not very experienced with that minigame, so i'll wait for others to suggest.