Gianluca, although there is no schematic for the iPad mini 4, this is a very similar configuration to the iPad Air 2 logic board. I looked at my donor mini 4 and cross-referenced with the Air 2 schematic and the components missing are ESD Suppressors / TVS Diodes (ESD0P2RF-02LS). You can find these from either donor boards or via an electronics wholesaler like Digi-Key or Mouser.
While it’s always better to replace these parts, they are not critical to the proper function of your device. They are there to filter spikes on the power lines.