It's very difficult for clubs to repeat the feat the next day. However, Paris Saint-Germain is an excellent team that will certainly earn its respect, but I also think they won't even manage to reach the final again. They got there thanks to a bit of luck.
Repeating the same feat in the Champions League is indeed very difficult, although not impossible, as it has also happened to a team like Real Madrid. However, for a team like PSG, it will clearly be very difficult to reach the final or win again there, because the competitive tension there is very different from that in Ligue 1. So PSG only has a chance to win Ligue 1 repeatedly every season, but not in the Champions League, where every team will always play their all-out to win.