Diamond can only kill someone if they choke on it.
Unless I am mistaken Veer has already eaten the Kheer that the diamond was in so if nothing has happened to him till now then he will be fine except for being poorer in his pocket !!!!
Actually, its a clever 2 prong plan that the ladies are putting into action, to force Pakhi to either accept Veer or let me him go:
So on one hand we have Jiji and Nandani trying blackmail / guilt trip Paakhi into accepting Veer (he has become absent minded, suicidal) ; and
On the other hand we have Charu telling Pakhi to break this relationship (first she said if you are not happy in a relationship then you should break it, yesterday she said its was conspiracy to emotionally blackmail Paaakh).
Weirdly their actions are having 2 prong effect on PaakVeer:
1. it is reinforcing how well these two know each other (as Paakhi said yesterday I was right there is no way Veer would commit suicide)
2. it allowing Paakhi to see the strong determined side of Veer (up to this point she only seen glimpses of it) who will not tolerate crap not even from her