#1 ... You will NOT bonk from sleep deprivation. You can ONLY bonk from a drop in blood sugar which is caused by lack of food. So don't forget to eat.
#2 ... You will be fine. LOTS of ultra-distance cyclist do ultra-distances with little or no sleep. Have a look over the stories on my site, for example:
http://www.machka.net/ Many Randonneurs (thousands of us) do 1200K randonnees within the prescribed 90 hours with less than 10 hours of sleep in that entire time.