There is no requirement right now to completely rebuild Aura components because Aura and Lightning Web Components can work together. They are completely interoperable.
I don’t think you should be intentionally building Aura (Lightning Components) any more. I haven’t read anything about Aura being deprecated yet, and I don’t expect that we will for a few more years. That being said, I think you should stop.
When will Aura be deprecated?
I think we’re looking at a 5 to 10 year timeline at least. Visualforce isn’t deprecated yet and can work with Aura and Lightning Web Components