Since the files in the 'Photos' and 'Videos' tabs of the Send menu are stored in the native Photos app, and the files in the 'Contacts' tab are stored in the native Contacts app, deleting Send Anywhere app does not delete the downloaded files.
However, all files in the 'Files' tab of the Send menu are stored only in the Send Anywhere app. Therefore, if you delete Send Anywhere app from your iPhone/iPad, it will also delete the files stored in the 'Files' tab. Before you delete Send Anywhere app on your iPhone/iPad, you need to move the files from the Send Anywhere folder to a different folder within the Files app. Be sure to back up any important files, as they cannot be recovered once deleted.