Paul Farquhar
Legend
In both Baldur's Gate 3 and Crown of Solasta one of the most effective tactics is pushing enemies into "bottomless" pits, which results in automatic death for both PCs and monsters. This is clearly the author's intent here. You might feel that it is unfair or unduly harsh, but it isn't incomplete.
Everyone has their own style of DMing. Whenever you run an adventure written by someone else you are going to come across places where they do things differently to you. In a simple situation such as the one described by the OP, most DMs can rule on the fly. In my game I tend to ask for a dexterity saving throw in that kind of situation. Or I might allow another character to use a reaction to grab the falling character. Which is definitely not in the rules, but suits the action movie tone I aim for. Someone who is more old school might well prefer "time to roll up a new character".
Everyone has their own style of DMing. Whenever you run an adventure written by someone else you are going to come across places where they do things differently to you. In a simple situation such as the one described by the OP, most DMs can rule on the fly. In my game I tend to ask for a dexterity saving throw in that kind of situation. Or I might allow another character to use a reaction to grab the falling character. Which is definitely not in the rules, but suits the action movie tone I aim for. Someone who is more old school might well prefer "time to roll up a new character".