Sorry, this is one rare time where I think you're WAY off base.
Baseball should be played outside. Teams and baseball fans have been doing just fine for 150 years.
Target Field is a gem. A roof would be a crime against humanity. People make the trip all the time.
And for everyone else...we're talking about a couple days of potential rain. Geez. Relax. I guarantee this isn't the first time it's rained in Minneapolis, nor will it be the last. MLB and the Twins will survive.