Twitter's mMAUs (monthly Monetizable Active Users) stands at 450 million. If they pay $8 per month, that gives Elon $3.6B per month. It will take 13 months to make $44B - the purchase price QED. Elon Musk is a genius.
As for you, my friend, your calculation is unrealistic. How sure are you that 450M users of Twitter will pay 8$ per month? You should always base your computation on the worst-case scenario. Then Based on my research the active users per month of Twitter is at 290.5M
Source:
https://www.statista.com/statistics/303681/twitter-users-worldwide/I don't know where you got the 450M users, Besides that you say that Elon Musk is a genius, that's normal because he is a businessman. And as far as I can see, he doesn't care about people, if it helps, he will get his money back. Elon Musk can be said to be one of those shrewd businessmen who will not allow himself to lose in his investment, he always thinks ahead. This is just my assessment.