One of the main benefits of playing Pyke is that he is able to "kill secure" and share kill gold with allies.
So ... take the kill...
Don't expect your teammates to help you. If they participate, they will get the gold and that is really what matters. If they don't, and you are able to genuinely get the kill on your own, they shouldn't really have anything to complain about.
They may get upset with you, but they are being stupid. All they are complaining about is their KDA, .. which in reality is unimportant in the overall scope of the game. If you have done your best to give them the opportunity to assist, you did your job. Don't miss out on the kill because you are trying to avoid getting grieved. Honestly, I would probably be more upset if you simply let the person walk away on 1% health because you were trying to give me the kill.
Something that I always like to keep in mind is, if the game goes to level 18 and full builds, .. KDA doesn't mean anything aside from someone's ability to gloat. It's "proof" that they carried.
So yeah, if people are complaining, as others have suggested, mute them and carry their ungratful asses to victory. (But try not to be smug about it)