Hi Nina,
Life is the name of glorious uncertanities, so everything is possible in here.
LSE is kinda weird, as for their MSc porgramme a high percentage person might be on the wait list and the low percentage guy on the merit list.
As for rejecting offers, the percentage is really really low, its generally if they are unable to make upto the conditions that was set for them, or if they get their admission deferred for another year or so.In which case a vacancy is created and a person on the reserve list is called.
I wish you all the very best and hope that u make it.
ANks