Something you may not know about Sion
If you kill a buff and your re spawn timer is up before your passive you will re spawn with the buff.
If you kill a buff and your re spawn timer is up before your passive you will re spawn with the buff.
I'm pretty sure that works with all champs. I seem to remember them changing it that if you were executed by monsters, you don't lose your buff
working as intended, if you get executed you don't lose buffs so it makes sense