I dont know if they will last but I dont think he will seperate from her specifically for his daughters.
It's a fact that Ella was treating him appallingly already before Bianca and things have obviously become even worse since then. To even have any remote chance of Ella behaving for 10 minutes he would probably have to give Alice all his money and more (and even then she would show him her cold shoulder, see 2021). This isnt a choice between Bianca and Ella, it's a choice between Bianca and no one. And I'm sure he knows it. This has never been about Ioan not focusing enough on his daughters, he did all this until august 2021 and it got him nowhere.
I can however see Bianca at some point removing herself from that situation. For her sake and because she may hope it achieves what you believe for him (no doubt deep down she does blame herself potentially)
I also disagree that they will accept his next potential partner. That one will be just the new evil witch that forbids daddy to give them cash and who wants to steal their money etc. It will probably not be as extreme as with Bianca because the first partner is always the worst especially when you believe they caused everything (not for children, but for the ex-wife, but Alice has basically groomed them to think like her), but it would be extreme. And I doubt Ioan will find many women that are as patient as Bianca tbh. Plenty of women would have actually assaulted Ella after how she behaved and after how she has treated her father the past years (keep in mind by then Ella is no longer a child so a future partner will have a lot less restrain to fight back) and plenty of women would probably make him choose between them and his kids.