So as I mentioned I would never delete a page without a redirect (even if that is a redirect to the homepage). If you do that, there will be a minimal amount of authority that you lose. There's no way to know exactly how much, but it should be marginal.
As for the referral traffic, I mentioned how to measure that above. But again with a 301 redirect, you will keep that traffic and if it is still relevant traffic, it should still add to your bottom line.