There are worse options than what happened to Newcastle - for example Union Berlin. They failed in the Champions League and miraculously remained in the Bundesliga, were very close to relegation. But I think that despite the fact that Girona lost several players, such a failure is not threatening them. I think they will be able to qualify for the 1/8 finals of the Champions League (in the new format it is much easier for newcomers) and then everything will depend on the draw.
Don't know if the new format will be easier for the new teams coming into the Champions League, basically it's a tough competition I'm not so sure about Girona but we don't know how they'll fare next season whether there will be any changes or not, but usually the underdogs won't stay up for long.
Prediction: I don't have much hope for Girona, it's a small team but even if it's a surprise there's no expectation because we know they'll lose at some point, their mentality of playing in the Champions League doesn't have much experience, because of this tournament the mentality of the players also affects it.
In the old format, if you were from the 3-4 basket, you would end up in a group with, for example, Inter + Bayern, and that would be the end of your performance (you could fight for third place and a ticket to the LE). Now, after each defeat, you will end up on a weak team (mostly, of course, sometimes there will be unpleasant surprises) and you will have a chance to improve the situation. Roughly speaking, earlier, to get to the playoffs, you had to be better than some top clubs, but now you will just have to be better than weak and average clubs. In my opinion, the difference is very big.