For a sump I'd probably just leave it.. I'm not sure if it is in the way or what your reason is for wanting to get rid of it, but if you can leave it you might as well. Then again, if you really feel the need to remove it, you'd probably be fine without it especially since you only plan on keeping it about half full..
If you do decide to remove it, I would try just removing it from the silicone instead of using a hammer. Crazy things happen with glass and hammers haha..