I have seen a few threads about "bad reviews here" or comments about "this game will lose blah blah players if this" and I could just care less. If people want to leave, then leave. I've played MMOs with small numbers of players, and it doesn't really matter as long as the servers that are still around are populated. You can go play WoW with it's 200 servers, but it's not going to differ much in population density per server(of another game with the same size world, for arguments sake) from a game that only has 4 servers. It just doesn't matter.
Now, money, many people say things about MMOs "failing". This is usually because the developers give up because they aren't making as much as they'd wanted, not because they aren't grossing off of the game. Warhammer Online's devs have said that despite the loss of players the game is not "a giant money sink" and "is profitable"(http://www.escapistmagazine.com/forums/read/7.223272-BioWare-Mythic-Swears-Warhammer-Online-Isnt-a-Money-Pit). They also said at one point that they could profit off the game even if it dropped to one server(this quote is from a couple years ago and I couldn't find a link for it, sorry). I know Mythic isn't as big of a company as SE, but it is a well known name in MMOs. Their first two MMOs were both very successful for their time(Darkness Falls and Dark Age of Camelot), they weren't a nobody company. Just thought I'd throw that in there in case anyone started talking about Mythic and didn't know about those games.
Anyway, my point is I don't think that FFXIV will ever be in danger of failing. If it were a separate game in each country it was in, then yes it may be in danger of failing in one of the countries, but probably not all. Since this game spans several countries I think it's playerbase will always remain a decent size. Anyway I've rambled long enough, gotta go buy some drank real quick lol.