A piece of elastic is about the most dangerous thing I can imagine putting around your cats neck, especially one with beads on it. Yes, it will break, and then suddenly your cat has a piece of elastic to play with and possibly swallow and possibly obstruct her intestines, and the same thing goes for the beads that are all over the floor now. Also, it will be very hard to fit elastic because it stretches so much... so how do you make it not too tight but at the same time not so loose that she can't get it over her head? I don't think you can. If it doesn't break it probably won't come off and that's just as dangerous. Best case scenario, if the need arises, is that it does happen to come off and leave, um 14k gold in a tree... but I wouldn't risk it and my cat doesn't even go outside.
They do make safety-stretch collars, but they are about half an inch wide and are elasticized nylon, usually, with a buckle. These have the same purpose as the regular breakaway ones in that if the cat gets stuck the weight is enough to stretch the collar so that they can slip out of it.
Breakaway collars are usually nylon (these are fabric) with a special clasp that won't come off (well, a lot of cats have spent hours figuring out how to get them off!) unless about four pounds of pressure is put on them, so if the collar gets caught in bushes or on a tree the cat does not hang.