Got the VPN back up the other day. It looks like the system got attached to the Basic Firewall set of filtering rules (and I am completey unable to see how, why, or where) and that seemed to be written in a way which was dumping everything which was going in or out. So, one rule to explicitly permit lz the ability to do any protocol (since just permitting TCP, UDP, and protocol 50 failed to work) later, and we have the tunnel back up.
However, the cable modem seems to be celebrating by dumping it's connection every morning. I had to cycle the power yestarday morning and this morning in order to get it to pass packets properly. The VPN survived the outage, amazingly.