I did the same thing you did for the exact same reason. I was putting on my Yakima pads and broke one of the tabs attempting to get it back on. I tried glue but it didn't hold and broke again when I tried to put it on. There is a good chance it is going to fall off without the clip to secure it but I would suggest leaving it on in the meantime. Water can and will enter that little spot of the roof without it. Who cares if you lose it if you need a new one anyways. I don't suggest gluing it to the roof rails, if you ever need to get the cap off you're SOL.
Suck it up, go to the dealership and get some new ones. When I put them one the second time I wedged a screw driver covered in a shop rag under the roof rails. Be very careful to not scratch your paint or wedge it to far under as to break anything else. I just barely lifted the roof rail and it the end cap just slid right on. Super easy! Thus avoiding another break.