MTGNexus

What happens if Kelsien, the Plague with deathtouch pings a creature and Kelsien gets removed before the ability resolves?

The game will use Kelsien's Last Known Information. So it will see that it had Deathtouch as it last existed on the field so the damage is coming from a source with Deathtouch. And you will still get your Experience counter since that is part of the activated ability and not a separate ability on Kelsien.