What happened with PSG and Chelsea has nothing to do with the league itself, it will not make PSG crumble or change, they will get the league title again. What it could do maybe impact UCL for PSG , because whatever happened there, could be something they should be caring about during the UCL period, if Chelsea figured out a way to beat PSG then it would mean they could do it again, and other teams could fix it too.
What Chelsea did to PSG in the FIFA Club World Cup is definitely demoralizing but I'm sure that Luis Enrique would have taken the lesson learnt to correct that fatigue that befell them. Instead of hindering them next season Champions League, it will even motivate them more and make them not to underestimate any team. Even in the French Lig 1, PSG is still the favorite to win it with little resistance from any team that might peak up for next season.
Overall the way Paris Saint-Germain lost to Chelsea was definitely demoralizing and I believe that maybe that fatigue won't build up in them because there is no doubt that if they can increase the amount of work and reduce the stress, they will probably return to their previous state. We have seen that some players from this team have stepped into the void and they have performed well at the international level, we should be sure that these players will probably start with a stronger morale because they have mastered the techniques of rising from the bottom to the top.