Nawaz Sharif is well-known to have friends in the Mid-East royal families. Saudis negotiated his release and sent a private plane to fetch him during Musharraf time. Thus even if we presume that the letter from the Qatari Prince is genuine, the funds were lent only because of Nawaz Sharif himself. It is therefore quite clear that without Nawaz Sharif being Chief Minister of Punjab and later the Prime Minister; his children could in no way be so wealthy.
However, it is also a fact that NS was himself not named in the Panama papers only his children. According to the strict letter of the law, you cannot punish the father for the crimes of the son.
This judgement neither completely exonerates NS nor disqualifies him, keeping both the parties semi-content. 2017 is one third over and the required investigation can easily drag on for another 6 months. Then even the disqualification will become meaningless because election will be around the corner and Shahbaz Sharif would be ready to take over the mantle with Hamza Sharif taking over Punjab.
In my opinion this is a political judgement keeping in mind sentiments of both the political parties.