As someone with some paternal English ancestry, and who is involved with English causes and friends... I can say that if any muslim terrorist would dare unjure, hurt or kill Harry, no moslims would ever feel safe in the UK. I'm not even joking about it.
As for Princess Diana, she was not killed by moslims. She was involved with one and then the conspiracy theories started. Not enough to create a wave of anti-Islam in the UK.
If however, a prince would be killed by moslim terrorists there would be chaos. And I think in a way the moslims know this, none of them have passed a fatwa against Harry have they?