Discussion with my friend: He plays carry. We get the first blood mid near first bounty rune.
He leaves the fight on 100 hp and decides to suicide himself to the enemy tower or Pos 4/5 to get back to his lane quicker and regenerated.
Is this the correct play?
Absolutely the correct play. That early in the game, the death gold bounty is about 150-200 gold, divided across all enemies if there’s no enemy hero who last hit. That’s approximately a creep’s worth of gold or less, which is negligible.
By suiciding, you come back with full resources, you don’t play scared because you’re low on hp/mana, you don’t waste regen items needlessly, and you don’t flirt with dying and easily giving your enemy gold and exp.