If Haytham Kenway leaves the battlefield before its last ability resolves, the target creatures won’t be exiled.

Auras attached to creatures exiled with Haytham Kenway’s last ability will be put into their owners’ graveyards. Any Equipment attached to them will become unattached and remain on the battlefield. Any counters on the exiled creatures cease to exist. When those creatures return to the battlefield, they will be new objects with no connection to the cards that were exiled.

If a token is exiled with Haytham Kenway’s last ability, it will cease to exist and won’t return to the battlefield.