The only advantage of Bayern Munich signing Ronaldo is that they will generate more money from the sale of jerseys. Signing Ronaldo will also require lots of money for Bayern Munich.
I don't think Bayern Munich need that, Bayern prefer to strengthen the line-up, they don't look like they are short on funds. Bayern need players who can make the difference and cover the gap left by Lewandowski, and Cristiano Ronaldo is still less effective for Bayern's needs.
I'm pretty sure of the signing of Sadio Mane but to maximize their desire, Bayern need more than what they have at the moment to partner Sadio Mane up front.
Bayern's achievements in the Bundesliga further reinforce the notion that they need new players up front