if i use siphoning strike, and the unit dies but is saved by zhonyas hourglass. do i still get 1 rune?

No — you do not channel the rune.

Siphoning Strike's "When it dies this turn" is a trigger that only fires if the unit actually dies. Zhonya's Hourglass is a replacement effect ("would die... instead"), so it replaces the death event entirely — the unit never dies, it's just healed, exhausted, and recalled to base (Core Rules 370.1.a.1). This is the same reason a unit saved by Zhonya's doesn't trigger Deathknell: death-based triggers require a real death. The delayed trigger never fires, so you get no rune.