[well... he shouldn't promise anything he can't be sure of delivering on. he can't just make a gate home for her - he's lost the use of dark corridors, and if there's a way to do that with a Keyblade he doesn't know it.

but still...]

If I can find a way, I'll do it.

Until then... I don't know how much this helps, but, time does flow a little differently between different worlds. If time's a factor, in whatever's happening that you need to get back so badly - well, I can't promise anything, but you might just have the time you need.