1 of 2 things most likely. either nothing happens and it gets hot, or possible much more likely it would burn up and start to malfunction or stop working entirely
not exactly an answer here but i did find this much, if you intend to fix the UE Boom by yourself you do void the warranty, so if you have a warranty it would be better to have them replace/repair it for you. unfortunately i could not find a video or tutorial on how to replace the rubber
i personally have never done this but here is a link showing what to do . https://www.youtube.com/watch?v=IZeOrsYw... it seems relatively easy from what i saw remove 10 or so screws from the bottom of the laptop, then very gently pop up the top half of the keyboard, then unplug the 2 wires connecting the keyboard part to the laptop. it doesnt show him putting in a new one but basically reverse order. do this at your own risk i suggest you have someone who is a little experienced with you when you do this. edit: if the link doesnt work search this in youtube "How to replace keyboarad on Asus X550 series keyboard replacement"