Can Kafka replace a database?

Nope

Kafka is not a permanent storage platform. It’s a streaming platform which can emit data close to realtime from variety of sources as topics. As such it provides a real time stream of data changes happening in a source. It also doesn’t comply primary properties of a database like ACID properties. Hence it cant replace a database. It can be used as a intermediate streaming layer between two databases. Alternatively it can be used to provide a continuous stream of data for real time visualisation tool.