The rat in Ratatouille will probably die within two years from the end of the movie

Rats don't live long, the first result on Google says that they live 2-4 years on average and the longest living rat in captivity lived to be 7 years old.

I like to think that after the rat's death everyone will treasure the good memories and start another restaurant of their own. But it's more likely that they'll be depressed and miserable for the rest of their lives without being able to tell anyone their story.