Is there a Standard card similar to Debt to the Deathless?
The cards from Theros, Born of the Gods, Journey into Nyx, and Magic 2015 (the sets that will be standard when Khans of Tarkir releases in September and whose contents are currently known) with abilities of the form "Each opponent loses n life.  You gain life equal to the life lost this way." are as follows:


Gray Merchant of Asphodel — life loss equal to your devotion to black when it enters the battlefield
Scholar of Athreos — life loss of 1 via a 2B activated ability
Servant of Tymaret — life loss of 1 whenever it becomes untapped
Tormented Hero — life loss of 1 whenever you cast a spell that targets it


There are no cards with this mechanic in Magic 2015, unless you count Covenant of Blood.