i have no idea why the site died and the DB crashed.
some data may have been lost. check this. i take backups often so hopefully any loss will be between 0-6 hours.
these are the only log entries i can find (mysqld):
151103 16:58:46 /usr/libexec/mysqld: Incorrect key file for table './smf209/smf209_sessions.MYI'; try to repair it
151103 16:58:46
Got error 127 when reading table './smf209/smf209_sessions'
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opened a problem report with SMF, FWIW: http://www.simplemachines.org/community/index.php?topic=540927.0