OleOle asks: What would happen to the fuel tanks, if they were penetrated by high energy shrapnel in mid-air?
Based on the many colleagues I saw shot down over North Vietnam with blast/frag missile warheads and AAA fire, I would expect the aircraft to burst into flames as it comes apart in a collection of small and large pieces.
However, while a big ball of fire could be expected, not every aircraft burns in this way. I would expect MH17 to catch fire, but it is possible that the aircraft might not burst into flames even after being hit with a relatively large warhead. Several combat losses I witnessed did not burn up in the air.
Judging from the pictures of MH17, it looks to me as though there was a big fire after the aircraft impacted the ground. I would say there was plenty of fuel remaining when it hit. I haven't seen any good photos or videos of the aircraft as it fell, so I can't say if it was on fire or not.