If the machine run the introducer down,what can i do

[Zooko Wilcox-OHearn]

That's right. If you have a backup of the introducer's private keys
then you could set up a new introducer that would have the same FURL.
If not, then you'll have to put in the new introducer's FURL to each
storage server and each client.

The multi-introducer ticket that str4d mentioned is ticket #68:

https://tahoe-lafs.org/trac/tahoe-lafs/ticket/68# implement
distributed introduction, remove Introducer as a single point of
failure

The state of that ticket is: "test-needed" — it is waiting for someone
to write unit tests that test the code changed by the patch.

Regards,

Zooko