I don't see how arranged or political "equal" marriages could happen in this era at least in the UK, just to keep the royal blood intact, that would end the monarchy pretty fast as well.
I don't think dynastic marriages are impossible in this era, see recently e.g. Alois of Liechtenstein and Sophie of Bavaria. In fact they are still pretty common precisely among
non-reigning royal families, who ironically seem to attach a greater importance to "keeping the royal blood intact" than the ruling families, perhaps to boost their pwn legitimacy.
I don't think either that dynastic marriages necessarily have to be "arranged", but I acknowledge that, nowadays, the involved families have at least to be engaged in some degree of "match-making" for them to happen.
There was a lot of casual speculation for example that Prince William could be matched with Princess Madeleine of Sweden as they are of the same age and both come from Protestant royal houses, but, when Madeleine was once asked about that possibility, she replied, much to my surprise, that she didn't recall having been even introduced to either William or Harry. If William and Harry never mingled socially with other Continental royal houses, how could we have realistically expected them to date a European princess?
I think if/when the Monarchy is abolished there will be a tremendous series of rows over who actually owns what. And that's if it's by democratic referendum.
Maybe it is not so complicated. The Queen's private property, like Sandrigham, Balmoral, or most of her jewelry, would remain private. The Crown Estate and the Royal Collection, as well as the currently occupied Royal Palaces, would be most likely nationalized, i.e. would become state property. The biggest contention in my opinion would be about the Duchies of Lancaster and Cornwall, whose status post-abolition of the monarchy would be unclear.
