I just got kicked from a game for being AFK while dead.
Yes. Waiting to respawn now counts as AFK.
The AFK warning gives you exactly 45 seconds to react before you get kicked, but the trigger depends on where you are. At the start of the match inside the base, the warning appears quickly. However, mid-game, it takes about 2.5 minutes of complete inactivity outside the hall of storms for the warning to even pop up. Since death timers in HotS never last that long, it is physically impossible to get kicked strictly while dead. Anyone experiencing this was definitely AFK way before they died. You are making up fake scenarios.