I have two tunnels from he.net to two different tunnel servers, one on my DSL, one on Cable, and they both work fine independently or at the same time (NPt helps there).
If they all went down at the same time then one of a few things had to have happened:
Your monitor IP pings were not going over the interface you thought they were
Upstream connectivity to the tunnel servers died (Happens a lot when someone decides to DDoS he.net)
Something else along the path caused the tunnels to drop
With quite a lot more information about your setup, it may be possible to speculate more accurately about the cause, but there isn't enough to go on there.