I can't think of a way to make a pushable which is also breakable respawn, but maybe you could do something with an env_renders and a gib shooter, and a passable button.
Make a passable/shootable button in the area of the pushable. If you shoot in that general area, it will render the pushable invisible, and shoot some gibs at you to simulate the box breaking.
To reset it, you'd have to render the pushable visible again at the end of the round--no idea how to do that--, and of course there would always be the problem that the invisible pushable would actually still be there after "breaking" it.
How do you make the box be pushed by bullets and not your body?
You might make a complex series for shootable buttons and make the box a func_train. Might be an interesting example map for someone to try
![:)](http://192.241.182.11/images/smilies/smile.png)