I had the same thing happen. I meant to delete some volume program I added which did not work with my xp system. I am not that computer literate and unknowingly I clicked the wrong thing and deleted my volume control. Somehow it actually did "reconstitute itself after a restart."
I tried to do system restore from a date before it happened, back when this first happened, and that did not solve the problem. In the past few months, somehow my older restore points have been deleted and only recent ones show up so I cannot try to do that again. I used to make restore points myself, and have no idea why they no longer exist. Then again, I have two virus software programs (Microsoft essentials and Norton anti-virus) which do their own restore points and I have a hunch it may have deleted my older ones considering Norton caused some major mess up, which resulted in them giving me an extra 120 days free of service.
It won't let me add it on add/remove, yet when I say to put the volume control box in task bar it won't let me and says "volume control system has not been installed" and says to add it in the add/remove. In addition, some other volume enhancer ac3 filter which worked several months ago, has not worked since my volume control got deleted. It is aggravating cause I cannot easily raise or lower my volume, cannot use my ac3 filter, and no volume control shows up on my task bar. Even Microsoft fix it center (windows audio playback trouble shooter) does not solve the problem. I tried looking up options online and even went into some core menu thing (gray border with white background and drop down menu on left where you click on items with codes and some with names and other things show up and you are supposed to look for certain things and change or delete it. I think its related to hard drives, programs, and files on the computer and in there, no volume thing in there at all like the computer options list I was given when I looked up how to fix this.
I do not have my cd disks since I purchased my laptop at a discount price from someone who programmed it to xp instead of vista (which I wanted). They never made me disks for my system. I tried to make it myself and it failed after so much time put into it.