Good advice so far - even after doing this as long as I have I cannot understand the reasoning behind putting a scope on such a gun and discarding the iron sight and not providing it when it is sold, or a buyer not demanding the original sight in the deal or a substantial discount for the lack of it.
I've seen it time and again. Personally, I have no use for a large, heavy revolver made larger and more heavy by the addition of a mount, rings, and scope since, I am led to believe by those who do so, that they "want to hunt with it". Having taken deer with a scoped Thompson Contender I can tell you that if you don't have a set-up akin to shooting off a bench rest (i.e. a pack, shooting sticks or convenient tree branch) it's an unwieldy contraption and not very handy as a hunting weapon used free hand. It's one of those that 'sounds like a good idea at the time' but in reality there are very few shooters who can successfully take advantage of such a set-up.
Personally, given the trouble it takes to round up a proper replacement sight I would consider such a gun worth at least 25% to 30% less than what a comparable one would sell for in original condition regardless of what kind of accoutrements had been hung on it to "enhance" it, but to each his own.
Unless it's a killer deal financially, I'd keep looking. There's a reason you see so many scoped revolvers for sale . . . YMMV