I bought Samsung Galaxy Note tablet and received 48GB of Dropbox storage for two years. I already had 22GB free storage so I can now use 70GB of Dropbox storage. After two years, my free storage will decrease back to 22GB. Then what happens to my data? I don't think they will just randomly delete my files to make it 22GB.
According to the Dropbox Help Site you still have access, but you will not be able to sync anything (new or changed files) until you get the space down to whatever you are actually subscribing to.