Hi Badali,
The short answer to the question is yes, it is possible to put the item back onto the window without removing the mechanism. I would recommend that you put it back, or put in something to guide the window. It will rattle around otherwise and won't go up and down satisfactorily.
I've done this (twice - don't ask why) and it isn't difficult, it's just a pain. Do a search on the site and it'll produce a load of good info about how to do it, and what to do. It'll also throw up some alternatives that I strongly recommend you consider - had I known what I know now I'd have gone down the route of replacing the guides with some felt guides.
If you stick with the orginal piece, take advice on the right glue to use. (I just used a strong epoxy. Just not the right one...)
JH