All the steps of the installation are saved during the install to /var/log/esxi_install.log
In order for it to survive a reboot - you have to copy it to a permanent datastore.
# copy %first boot script logs to persisted datastore
cp /var/log/hostd.log "/vmfs/volumes/$(hostname -s)-local-storage-1/firstboot-hostd.log"
cp /var/log/esxi_install.log "/vmfs/volumes/$(hostname -s)-local-storage-1/firstboot-esxi_install.log"
I use this is all my kickstart builds (Source - http://www.virtuallyghetto.com/2012/09/automating-esxi-51-kickstart-tips-tricks.html)
Another option you might want to check is removing the reboot statement in the kickstart file - which will allow you to go into the console and check the logs - before they are purged.