From my own experience, once you have purchased/downloaded an app you can install/re-install it on devices without any restriction, but you would be wise to kee

From my own experience, once you have purchased/downloaded an app you can install/re-install it on devices without any restriction, but you would be wise to keep a copy of the .ipa somewhere. I downloaded the VLC app on my iPhone before it was pulled and have since been able to install it onto an iPad I bought last month no problem. Obviously it won't be updated so the problem of future compatibility is still an issue.