You don’t need any hindsight to know what the FDP is going to do when you invite them into government. They will do what they have always done: Maximally corrupt clientele policy for the 1%. That’s what they did the last time they had the chance. And the time before. Whenever they do that, they’ll of course lose popularity, but that won’t hurt them, because the “donations” from their rich clients will keep flowing. They will simply lay low for a few election periods until the public has forgotten what they did and run a flashy campaign specifically targeting dumb first time voters to get back.
If there are no contingency plans ready to be enacted for that idiot becoming US President again, then shame on every EU country that didn’t prepare any. This Problem was foreseeable well before the first time he got elected, at latest, when he took office for the first time.