During à summer drought, units routed at the end of a battle round are they destroyed immédiately or are they destroyed after the end of the battle ? In second case they can be rised immediately by a Rally Cry during the battle (or counted if hexagonal),

The drought card reads: "Any units or heroes that become routed during this season are instead destroyed." (my emphasis)

The units are not routed, so they can't be affected by Rally Cry. They are destroyed immediately.

Yes but in that case Summer drought is too much powerful: you cannot hope defend an area where you have (for example) 8 units with a lot of Hit Point against 10 or more ennemies units because as soon as your opponent obtain a Routed result he kill automatically a unit of 4 HP (for example) and you cannot even use a Rally Cry !

Not sure that it was the intention of Corey...

You get to choose which units you rout, however. Choose carefully...

(Plus, the enemy suffers from the same card, his "routed" units will be destroyed as well).

Indeed.