It's interesting to watch how quickly candidates are dropping out after Iowa and New Hampshire.
Since Carson and Gilmore won't be in the debates it isn't that important, but it will be newsworthy none the less when they finally go, although who knows if Gilmore stays in til the bitter end.
Rubio isn't likely to drop out before SC, nor are any of the others.
Carson will be in the next debate if he places fifth or better in an average of national and South Carolina polls. That's perfectly possible. He already received more than 3% in Iowa, so he doesn't even have to worry about the second prong of that test - getting over 3% in the South Carolina or national polls.