Since the platform conversation continues, I'm going to reiterate what I said previously a bit more clearly for the Linux/Mac folk, especially after refreshing myself a bit on the code: as long as Curse at least provides a direct download link to pack zips as they've suggested, then anyone (including FTB) can continue to maintain the existing cross-platform launcher.
Best case scenario is Curse agrees to let FTB host all of the necessary data for this launcher to continue working until they make an alternative, or, FTB finds some alternative hosting to do so, and nothing changes for people who need to use this launcher; FTB just has to modify the launcher from using Creeperhost to Curse (or wherever), which should be trivial.
Next best case scenario is that Curse at least provides a direct download link to modpacks. The current launcher would now have to be modified slightly, to separate where launcher data and the actual modpacks are gotten from, since
currently they appear to all come from the same server. The launcher data mostly consists of some XML with info about the packs/maps/etc, and images to represent the packs, which is all tiny stuff and could be hosted nearly anywhere. The launcher would grab the packs themselves from Curse's servers, however.
Not-so-best case scenario is that FTB drops all support for the current launcher, but Curse still provides the direct download link. You'd still need the aforementioned modified launcher to separate launcher data from the modpacks, but you'd also need a community volunteer to maintain and host the XML data. The packs themselves would still be safely hosted on Curse. Best way to modify the launcher in this scenario would be to add in a config option to specify where the launcher data comes from, in case that has to change at times (another volunteer takes over, etc).
Worst case scenario is FTB drops all support for the current launcher, and Curse doesn't provide direct downloads. Where there's a will there's a way, and I'm sure it would still be possible to make the existing launcher work one way or another, possibly even through the API whenever that happens. But you're at a point of diminishing returns now. Even the previous suggestion of a community volunteer maintaining pack data isn't a reasonable long-term solution.
At the end of the day it's just mods and configs in a zip file. There's plenty of places that do it if you're not able to get them from here.