Yes to keep, because I worry about what would happen to all their tenants who live and farm on Crown / Duchy land.
I worry about all the farms, forests and commercial enterprises on that land and in those Crown properties which, upon being sold (out of interest, who would we sell Crown Land to? The Chinese or the Russians?), would possibly have to lay off employees or cease trading.
Because I would worry about the ~1200 people (and that's JUST the Royal Household staff - what about the military regiments like the guards and Household cavalries, for example?) that the Queen currently employs.
I worry about what would happen to the hundreds (thousands?) of charities that have the royals as their patrons and receive much-needed money from them.
I worry about what would happen to one of the most significant art collections in the world. And how much of our heritage would be sold off. Art, jewels, castles...
I would worry about the impact on our tourist industry and how much money and how many jobs would be lost there. On any trip to London you sell those souvenir stands and newsagents selling everything and anything with Beefeaters, crowns, guards and palaces on. Tours of Royal London. Royal mugs, coins, everything!
You might win an ideological victory by making the UK a Republic, but I think there'd be one hell of a lot of pain first.