If you do not have an iOS device or a machine running OS X to open your IMOVIEMOBILE file, you can still access its contents. First, copy the IMOVIEMOBILE file, rename the file extension to "zip", decompress the file, and the project content will be in a folder called "Assets." You can then open the original content in a video editing program.
It's not rational, but I'd like to note how angy I am with myself in retrospect for not looking this up before. I have literally given up on old project files because I assumed the video was unretrievable and then... I just did this on my iPad in a matter of seconds lol.