I doubt that they will loose many customers at all.
Guinness drinkers may cry into their pints about the closure of St James' Gate and may say beer just isn't the same from the new place, but they will still drink it.
What else are they going to drink? Beamish? Murphy's? No, they'll take what they are given, just like they did when it went from cask to keg with nitro.
As to the foreign trade, as long as it's brewed in Ireland and they keep their existing tourist trap in the area, no one will care.
[quote:3a08f56k]Sure while they're at it, why not sell the GPO and TCD and turn them into apartments also. I'd love to live in one of my old lecture theatres <!-- s:) --><img src="{SMILIES_PATH}/icon_smile.gif" alt="

" title="Smile" /><!-- s:) -->[/quote:3a08f56k]
That's a different issue. When it comes down to it, a brewery is nothing but a factory.
If you want to go into Trinity College or the GPO, you can do so. Try having a look around St James' Gate; see how far you get.
The Guinness brewery is a huge area of land that is effectively a barrier to people. A huge, high walled block of nothing, that you have to walk around. Imagine all of that quayside area opened up, with flats and businesses, so you could walk through it.
Nostalgia may tell you it's a bad thing, but I think it will be a good thing for the city.