It all depends on the exact infrastructure, of course.

If the NA and EU servers are "that bunch over there" then yeah, NA will have to at the very least get turned off for a while.

If the NA servers are the bunch on the left, and the EU servers are the bunch on the right, NA shouldn't necessarily be affected.

To the Americans that seem upset they might lose a day or two in the game because Europe gets a quality of life upgrade, though? Suck it up. We've dealt with latency that made a lot of boss fights harder than they should be since 2.0 went live, it's time we got the EU servers located on the proper continent.