Personally, I think that searching for possible consequences of talking during chazarat hasha”tz such as losing one’s place in olam haba is not addressing the point. We do not understand such consequences of our actions.
However, we do understand other consequences of our actions. If we talk during chazarat hasha”tz, or kaddish, we are negating our entire reason for davening with a minyan. The whole idea of tfila b’tzibur is the “tzibur”–and talking during the parts of the davening in which you are represented by a shaliach or others negates that concept.
If one has difficulty concentrating on these parts of the davening, bring a sefer. Learn a few mishnayot. It may not be what you are there for, butr at least you will not disturb others.