Indeed. The Catholic-socialist stance that they have is very electable (especially the pre-2005 version which wasn't far away from Jarek's Centre Agreement back in the day) - but they absolutely cannot win with Kaczynski or some of the other maniacs as the leader. Kaczynski also seems to be very much determined to hold onto power at all costs - even if it's at the expense of the party.
But - you have to remember that if a new leader "softens" the image, they'll lose voters to Solidarna Polska. The old LPR voters will gravitate to whatever party offers them the most extreme option - and there is a good 5-10% of voters with similar views.
I think the media has played a big role in completely assassinating any credibility he had [no doubt PO fans will say he did this himself] but that is beside the point.
He brought it largely on himself, yes. If he hadn't spied on prominent journalists, hadn't waged war upon media outlets and so on - he would be in a far better place now.
The key is, it seems PiS is never going to get over 20 something % with him in charge.
They will get around 25-30% of the vote with Kaczynski as a guarantee. But Kaczynski is so hated by the other party leaders (Pawlak, Tusk, Miller and Palikot) that there's just no way they'll ever consider a coalition with him. Look at what happened in the Podkarpacie Sejmik - PO/PSL/SLD joined up to put PiS into opposition in one of their heartlands.
PiS needs a different leader so that they can gather more votes and perhaps talk less about the plane catastrophe and more about how they plan to improve life for people on economical grounds. If they do get power they will obviously have more power to investigate the plane crash and a real PiS supporter would know they have not forgotten about it, I just do no't think that it should be on of their main election messages as it does not seem to get through to a lot of people right now.
But don't forget - people also know that if they get power, they'll immediately go on a witchhunt against anyone who said anything against them. Look at what you've said - they won't forget about it. People remember how PiS behaved in power with witchhunts - they're also very aware that the party has always had issues with needing to take "revenge".
Their only hope right now is for the opposition (to PiS) to break up into many small parties who can't agree a thing. Can't see that happening right now - PO has very strong party discipline, for one.