Krallu, your friend will be perfectly fine on LOT. However, please take care on the journey to or from the airport, as Polish roads and Polish driving standards are different from those in Sweden.
The difficulty of travelling between Polish cities by road (a bit dicey) and rail (very slow) has been met by new services from OLT Express, flying ATR-72s and A320s on domestic routes. This airline now provides for day returns between places like Gdansk and Krakow or Poznan, which haven't been possible on LOT domestic services.