I'd say try charging the battery just to rule that out as a possibility... the battery went bad in my wife's 2015 Chrysler 200C, it tested good a month ago and Monday just stopped holding a charge. It was a warrantied part, but a new battery cal still go bad.
There is a fusible link in the cable going to the starter, its right up next to the starter, that could have blown when the battery got hooked up backwards. I'd say try jumping that fusible link with a jumper cable from underneath the car on jack stands, obviously being careful not to get your hands caught in a bad place and have two helpers to keep things from getting "too" dangerous... one at the passenger side to pull the jumper cables off the battery after, and one to try starting it after you bypass the fusible link.
If the starter turns the engine over, it's the fusible link. If not, it'll most likely be the starter itself.
