You don't need to worry about Keep. It's part of G Suite core services, which means corporations have long-term contracts with Google that basically guarantees it stays around.
Not to mention that Keep is deeply integrated with Gmail, Cal, Docs, etc.
No matter how lightweight of a tool it may seem, Keep isn't going away. G Suite is very conservative and careful with changes they make around their core services.
"Conservative" is one way to say it. Perhaps another way to view it is that development of some G Suite core apps has stopped [0], which should perhaps give one pause.
