I understand that an unsubscribed TiVo with the current 2.5.x software can make timed recordings just like a VCR although I've not been able to verify this because my subscription is active.

It's discussed here in terms of backdoor codes (from a link that dbrashbear posted in another thread), here's an extract from that site:
C-E-C Skip-to-end - Turns on "Boat-Anchor" mode. This convinces the TiVo that it should behave as if it has no guide data. Boat Anchor mode is automatic when the unit runs out of guide data, so this is probably only for testing purposes. A bit useless, really.

Upon reflection, regarding an earlier post here, my guess is that the subscription part of TiVo must surely be the real money maker and as such, even if TiVo (the company) went down, the appointed receiver would regard the subscriber list as an asset and sell it on. I wouldn't like to guess if that also applied to those with the lifetime subscription.
Additionally the TiVo community forums, although possibly just the reputable ones, ban any talk of service theft. Perhaps if the worst happened they would lift the ban and which would facilitate the community creating it's own TV guide.