The leaders being arrested doesn't mean the FBI will just...stop.sx os was not created by two people any more than atmosphere was created by two rat children.
It's more likely they'll go after anyone not based in China.
And new features or bugfixes for something other than just supporting the new firmware are already very infrequent from Xecuter.
Atmosphere is open source so even if SciresM is arrested (very unlikely), anyone could continue it.