Can hyaluronidase make your lips smaller than before filler?

Hyaluronidase injections can dissolve hyaluronic acid fillers. It can also dissolve our skin's natural hyaluronic acid but it is not permanent. Our own HA is continually replaced and within a day or two would return to normal. Your lips would not be smaller than before.
It is important to take pre treatment photos since it is difficult to remember and compare after treatment.

This is a tricky question. I think much of it is related to the fact that after a while when you have had lip fillers, you get used to having lips that are a certain size, and so to dissolve filler = smaller lips, with some skin laxity, which can feel scary and like you have dissolved too much.
In reality, we replace our own hyaluronic acid regularly, and so any that is dissolved should be replaced fairly quickly. In most cases, unless the skin of the lips has stretched so much that it leads to droopy skin, it should not dissolve more than what was put in, BUT as we age, our lips do flatten and lose definition and if it has been some years this is what we may see compared to our pre-filler size.
At the end of the day, removing filler, even if we dislike it, can be a psychologically taxing process and so it helps to be prepared to have some placed again once dissolved if needed. All the best and please choose your injector wisely.