Or picture a tree. It grows and serves a ton of purposes. It eventually dies, becoming soil and nutrients for new things. It continues on in a way as it becomes a part of those new things, but that specific tree is gone forever.
Picture a river. It's important as a food source, habitat, a power source, potable water, etc. It's vital and important. There needs to be water there for the river to function, but after a cup of water serves its purpose, it eventually ends up in the ocean. The river remains.