Unfortunately the answer is NO. If a recording is deleted by a user, or because the Series Manager is set to only keep a certain number of episodes, it is kept in the Recent Deletes folder (like a computer's recycle bin) until it is overwritten by another recording. In this case you could just go to that folder, select the recording and restore it. But when it is deleted by the DVR to create enough hard drive space to record a new program, the deleted program is immediately overwritten and can no longer be recovered.
Here are your options to prevent this from happening in the future:
As for the recordings you are missing now, you can try searching for them in the On Demand menus, or going online to sites such as Hulu or the individual network sites, or there are pay services such as Netflix.