Edit: I misinterpreted your question. I know it is possible for single modules:
http://requirejs.org/docs/api.html#errbacks
With this technique, you could create a module which would verify each module's existance:
loader.js
define(['a', 'b'], function(a, b) {},
function(err) {
if (err.requireModules) {
for(var i = 0; i < err.requireModules.length; i++) {
requirejs.undef(requireModules[i]);
requirejs.config({
baseUrl: BaseUrl + 'default' + '/js/'
});
require([requireModules[i]], function () {});
}
}
});