Also, what would happen if they lost again? Would Jarosław Kaczyński step down from the leadership and if so who would take his place?
If he does, I would wonder if PiS continues to exist. It is unlikely to, in my view, without JK.
The British political scene is different than Polish. Our parties except the SLD and the PSL are still ephemeral. If Poland did not loose independence in the 18th century, we would have most propably a similar dual-party system just as basically the UK has at present. Our parties would have been deeply rooted in the past and firmly established for a long time. One of them would have certainly arisen from the the "Society of Friends of the Constitution" formed in May 1791, shortly after the adoption of the Constitution of May 3, the other would have been formed by their opponents and would most certainly adopt the word "republican" in its name.
We would have also had a constitutional monarchy which, similarly to the British one, would be taking its origin from a German House, here the House of Wettins (member of this House was named by the Constitution of May 3 as hereditary King of Poland and Grand Duke of Lithuania). But, as history took a different course, we have neither of these and all our parties are subject to change, defragmentation or split as it happened in the near past with AWS (Akcja Wyborcza Solidarność) or KDL (Kongres Liberalno-Demokratyczny).