No, Garber wants
24 teams maximum (see question six). New York will almost definitely get the 20th team in 2013, and from there, things will likely go much slower as the league looks for committed owners it those markets. They're also supposedly exploring moving Chivas to San Diego or Riverside/San Bernadino to cover an additional prospective market.
For future expansion, they're looking at...
St. Louis
Atlanta
San Antonio
San Diego
Detroit
Miami or Tampa
Milwaukee (supposedly, I think this is pretty unlikely)
Ottawa (Melnyk was supposedly interested in a team, but it's more likely that it will be a D2 side playing at Frank Clair)
If ownership with deep pockets and an excellent stadium setup (meaning the owners also control the venue and are able to book other events there), then MLS will add beyond those 20 clubs, but there is no guarantee.
I see no reason why the league would be in trouble. All the owners have pretty deep pockets, every team (except D.C.) either have a club-owned venue or plans for such a venue by 2012, and all but Seattle and New England will have soccer-specific venues. Payrolls stay low and TV coverage is slowly improving on basic cable packages. The league plays a very marketable style of attacking soccer. Not to mention the remarkably inexpensive tickets that many markets have.
As long as the Islanders stay on Long Island, whether it's a renovated NVMC or the Barclays Center or an yet-to-be-constructed venue in Queens, I'll be satisfied. They've made too much history on the Island to leave because of politics.