It should still be in your purchased apps. You can check first:
Open the App Store app > Updates > Purchased > make sure Mincraft is in the list
You can download it directly to your library also:
Open iTunes and go to the iTunes Store on your computer and click Purchased in the Quick Links section on the right > sign in if prompted > Apps
As far as the data, I am pretty sure (but not definite) that Minecraft data resides on their server not on the device. Do you sign in with a username to use it? If so chances are good that the data is on their server. Either way, if you backup first then you will be able to restore if need be. Although the saved data will do no good if you can't open the app.