PSG were once very desperate to win the Champions League trophy, and now they have it, and I think that has definitely made their mentality even stronger, so I think they do have a chance to go back to back next season. It certainly won't be easy because the other big teams will definitely be making more thorough preparations (especially Real Madrid and Liverpool who are currently very active in the transfer market), but that doesn't mean PSG can't win it back because in football anything can happen.
Paris Saint-Germain was already crowned UCL Champions in their minds because this is the mindset Luis Enrique embedded in his players. He never relented, he had good opportunity to come in for winning, knowing what he's accessible for his team, they became competitive from the very moment they got qualified from the group stage. PSG fought so hard to come across these elite teams and still manage to triumphed, I won't call it luck but consistent epic performance.
Paris Saint-Germain are also doing really good in the Club World Cup. Watch how they thrashed Atletico Madrid as if they didn't play an elite side. Common brother, we're talking about one of the best team in Spain managed by one of the most experienced manager, Diego Simeone.