I’d imagine the investment caused by the EU funding may well have generated a fair amount of non-EU money that the park can use; from what I can gather, Energylandia’s visitor figures have risen fairly sharply (they’ve been over 1 million for a few years now, and I think they may possibly even have exceeded 1.5 million and started closing in on 2 million in 2019), and trip reports suggest that the park is often pretty busy, so I don’t think we have a Hard Rock Park-type situation here where the park isn’t attracting guests and can’t fund itself on its own.
From what I can ascertain, Energylandia will have no trouble being a self-sufficient park. They get fair guest figures, and the initial EU funding really got the park going in a big way.