I was sent my hero as RAID to oasis.
And then he die ?!
I thought only send as attack is dead ?! I thought hero never fight to out of hp as RAID ?!
An attack (or a siege) is always fought to the death
A raid the attacking units come and then attempt to leave, but this isn't always possible in case of an overwhelming defense.
The wiki actually has pretty good info of this:
"The troops will do battle until the sum of losses on both sides is 103.2%."
Unless there is very few troops there this will almost always spell disaster for a solo raiding hero, with few escorts though a 100 hp hero should come out alive most of the time.
That being said it's pretty questionable to solo raid with a hero in the first place as he can't carry anything by himself, best send full attacks and kill the enemies outright.
Always use the Combat Simulator when deciding if it is worth while to attack oasis'.
Basically you thought wrong. Raiding Oases is not just free Res & XP - you take damage. Take enough and you die.
I'm not 100% sure wether this rule still exists but I believe the hero dies if he loses 90 of his hp at once, for example from 94 to 3 hp (= 91 loss). However, a raid is a "cheaper" attack mode, the troops search for resources primarlily - if necessary they hit enemy combattants, but they'll attempt to leave as soon as possible - explained via storyline. The maths are simple, a normal combat is calculated and the losses are redistributed such that the sum of losses is 103.2%. Consequently you need to defeat at least 13.3% of the oasis' troops with your hero if you want to survive him (if he has 100 hp before) when raiding.
However, attacking with your hero only does only grant you experience - even if you usher all troops out with only your hero the following troops can't steal any resources. This is because an oasis' storage capacity is determined by the amount of animals living there. Each animal grants 50 storage capacity - if your hero kills all animals it's like destroying the storage - all resources are lost and you can't raid anything anymore.