They're purely a tourist attraction in the UK now. So they won't be gotten rid of any time soon.
The "tourist attraction" argument is old and tired.
Most European countries have abolished monarchies and France, Germany, Austria and Switzerland (as examples) have a high turnover in terms of tourists.
Versailles is one of the most visited attractions in the world.
The people who come to the UK because of the Windsors (and esp those who come for their events) are far and few between.
If the Windsors were abolished, the UK would benefit from tourism more than it does now, because all the palaces could be opened to the public, all year round.
Lists with most visited attractions in Europe only ever feature museums in Britain. Not even Buck P makes the cut (and Buck P is just the public facade, the real seat of power is, as it ever was, St. James's).
Who's ever gone to Denmark or Sweden because of the royals??
The Danes like to claim that their royals are a tourist attraction (like people in the UK say about the Windsors) and yet I know of no one who went to Denmark because of the Glücksburgs, in fact I'd say that most people who go to Denmark aren't even aware of the royals there.
The only purpose they serve is drama. Real life soap opera in the plush setting of palaces and that's it.
In terms of philanthropy, when Kate became patron of EACH donations went down. Papers/Magazines didn't sell with her on the cover.
Complaints came in of too few appearances and she didn't have that many patronages to begin with. Some she hadn't visited for years.
As pointed out above, having a royal patron does not increase donations and as seen in the past can even lead to a decrease in money raised, they are not tourist magnets, so what the heck does it do having them as patrons?
Austria and France got rid of theirs a long time ago, which didn't make a dent in people's interest in the history of these countries. The Windsors being "historic" or "living history" is therefore also a rather poor argument. For those interested in "living history" you can still follow the Habsburgs and their ilk. Some of them have good careers as historians (to keep their family's past alive), which is infinitely more interesting (& valuable) to watch a docu in which they participated and offer their unique archive than watch some "royals" blather on about current issues when they are the epitome of hypocrisy (the Cambs announcing K's 3rd pregnancy and Will then giving a speech how everyone should have a max. of 2 kids or the Ssexes blathering on about the environment and then travelling continuously via private jet even ironically to a useless environment conference which could've been done via video link in the true spirit of environmentalism (we all know it was really to rub elbows)).