Eliminating the monarchy would have absolutely no effect on the revenue from crown estates. It isn't private property, but owned by the crown. Who owns the crown? The nation. It wouldn't revert to the Windsor family.
That it is personally owned by the royals is a myth supported by the coronation ceremony and the media. These lands are from a time when the sovereign had more financial responsibility for running the country.
Who owns The Crown Estate?http://www.thecrownestate.co.uk/about-us/faqs/
The Crown Estate belongs to the reigning monarch 'in right of The Crown', that is, it is owned by the monarch for the duration of their reign, by virtue of their accession to the throne. But it is not the private property of the monarch - it cannot be sold by the monarch, nor do revenues from it belong to the monarch.
The Government also does not own The Crown Estate. It is managed by an independent organisation - established by statute - headed by a Board (also known as The Crown Estate Commissioners), and the surplus revenue from the estate is paid each year to the Treasury for the benefit of all UK taxpayers.
To explain further, one analogy that could be used is that The Crown Estate is the property equivalent of the Crown jewels - part of the national heritage and held by Her Majesty The Queen as sovereign, but not available for her private use.