The idea about microservices is that they are small and self-contained. This makes them easy to rewrite completely. Now I wouldn't say it is the goal to rewrite them all the time, but it is not a bad sign if some of them get rewritten occasionally. Microservices are somewhat new and a lot of architecture and infrastructure is being built around it. Companies like Netflix and Uber take the lead in this. Susan Fowler wrote a book about this during her time at Uber, you can find it here:

http://shop.oreilly.com/product/0636920053675.do