I have fixed zips by squeezing them with pliers. I wouldn't carry pliers on a trip to deal with this remote possibility though. I don't think I need pliers or would carry them on a backpack trip, but do carry them when weight matters less (paddling) or if I am fishing, or if I am skiing and may need to fix something there. I use the tiny light scissors in my med kit if I need scissors.
I do like having a real knife though, and to me, if you are going to actually use the knife blade, having the blade lock is a very important safety feature. A weakness of the knife blade on most of the multi tools is that they don't lock, or they lock poorly. Currently, I have the SAK one handed trekker, which has a large locking blade. I also really like having the saw if I may make a fire, and the OHT has a great saw.