Hardware cannot be fixed with software. I don’t have much experience on the Mini 4 but I wouldn’t be surprised wifi and cellular antennas got damaged while removing the glass to replace the screen, it may happen when one has little or no experience with iPads. I would buy it but I can fix the antennas myself..can you ? If you’re not ready to use it without wifi and cellular, you have to add the costs of parts and repair to you initial purchase price. You may try a full restore just not to leave any chance out, but chances a restore or Cydia will fix the issues are very very low.