That's not a bad way to put it.
The metaphor works better if you imagine the ball pulsing, getting larger and smaller, with a gradual trend to shrinking.
The initial size of the ball is a function of how much a part of your daily life the person you lost was. The trend toward getting smaller is a function of time and willingness to fill your daily life with other things / people / experiences. This willingness doesn't imply a desire to forget, either.