A sunspot is made of plasma tied to tangled magnetic fields. These magnetic fields have energy but less mass density than the surrounding solar material so they are buoyant - they "float". Think about an ice cube in a pan of water... it floats to the top! The bigger the ice cube, the longer it takes to "melt", and so it is with sunspots. Some are short-lived (just a few days) but some can last for a full solar rotation (27 days), or even more. But even though it is still there, it likely has changed in shape or size. Some Chinese scientists reported a sunspot group that lasted five solar rotations! (Chin J. Astron. Astrophys. Vol 5, p77-86, 2005).