Now Kaczyński and his base are getting too old.
Precisely.
Every year PiS's voter base decreases and democratic parties' voter base increases. Kaczynski and his thugs are already in the dump of history, they just haven't realised it yet.
once Kaczyński is gone...the party will explode
And will get fragmented into many smaller bolshevik/menshevik parties, with tens of little kaczynskis fighting for limited power in their tiny coach party, bitter in defeat, antagonized against one another and completely and utterly unable to unite again. That's what you get when you put partia ahead of patria.
Happy days for Poland. Happy days for the White Eagle. Happy days for all patriotic Poles.