If things are still as DTV expects them to be inside, then odds are greatly in your favor that they will not want to piss off a loyal customer (you) who sends them a check that they cash every month.
The "seal" is often not even sealed down on models I have had, out of the box. It is also pretty easy to unglue with a hair dryer and an exacto knife, if you really want to go there. I think actually destroying the seal might want to make them question why it is destroyed or missing, but all of that is probably a non-issue as long as the HDD is still intact.
Also, sometimes a "dead" DVR is really just sleeping. As a last resort, unplug power for a few hours, then plug it in, and wait. I once was mentally writing the obituary for a HR20 that appeared to be dead, but about 7 minutes later it rose from the dead like Lazurus. Sort of like a stiff in the morgue sitting bolt upright and scaring the bejeezuz out of the medical examiner.
One thing I have been mulling over is going back to OTA recording when possible, since reportedly those recordings would be portable between DVRs.
Also, if you have a DVR that fails to connect or record, but still plays back, a SD DVDR with a HDD is nice to have, especially if it can do 16:9. And since the source (the DVR you are dubbing from) is pristine HD, the quality is still pretty good when dubbed; just a little loss of resolution, which is better than losing a pivotal episode of a serialized drama you have been recording all season.