>I applied those patches to my -current sources and installed the new
>pppd and chat.  It did not seem to help.  It is still reliably the
>case that when the modem drops, pppd fails to notice and die as it should.

You probably have "local" (or at worst, "softcar") in /etc/ttys for that line,
right?  (Otherwise you couldn't have gotten pppd to work at all).  You'll
need to take that out to get pppd to die on hangup.

(This works for me here under 1.0).

--Ken