If at all the final has to be moved out of Mumbai, first of all, even before choosing alternate venue, BCCI should BANG Shiv Sena people, who are responsible for it.
They've renovated Whankhede by spending loads of bucks and losing many matches, that too, just for World Cup Final, and if it moves out due to silly politicians, its absolute ████! The final HAS to be at Whankhede!
And if at all, the situation demands change in venue, I'd choose Chennai or Bengaluru. Chennai should be given first preference cause 3/4th of the stadium has been recently renovated, and we can expect a house full for the final, ignoring the worry of India making it into final. If not, Bengaluru is perfect alternate venue. We've seen the crowd, for the England v Ireland match, which clearly says final will be a house full affair.
KSCA couldn't renovate the stadium due to traffic and parking constrains. The stadium is at the heart of the city and parking has become a uphill task for the cops at Bengaluru. And traffic is diverted for every 100 meters in Bengaluru due to the Metro works. If at all Chinnaswami Stadium would have been renovated, it would have easily grabbed the hosting final.
If Mumbai, Kolkata, Chennai, Bangalore and Delhi dont get the final, then Mohali should get it.
Mumbai>Chennai>Bangalore. No other ground is fit for hosting the final!