I can see three ways to handle this issue. There are probably others I'm not thinking of.But that always happens! You never, ever run in fear between hazards, or past them, you always run into them! Sometimes multiple times (if you save the first time and there's enough forced movement)!
One is to give it to the player. In which case the hazard will always be avoided, unless something else very odd is going on in the situation.
Another is to make it random. This would be the Gygaxian ideal, I think: it's player skill to avoid running in fear, but once you do the dice determine what happens to you. Sometimes you'll fall into the pit, sometimes avoid it, but there is no dramatic rhyme or reason to it.
The third is to give it to the GM. Which is what the Deathlock Wight (and 4e more generally) does. Of the three ways, I think this one maximises the likelihood of dramatic logic governing falling into the hazard. If it is getting too boring, or too deadly, the GM is always free to do something different. Or to switch to random resolution and roll the die in front of the players (I'm sure I've done this occasionally when the Chaos Sorcerer has pushed his allies on a 1 - the rule in our game is that this is a GM's push, not a player's push.)
I guess a fourth option is to give it to the Deathlock Wight, whom the GM then plays as an NPC. But that would strike me as silly - the forced movement, here, is running away, not being literally pushed by the wight.
I think that bringing out the difference between 4 and 3 drives home the metagame character of the power. Again, for me that is a virtue. Of cousre for others it's probably an objection.
They roped themselves together because, before they knew there was a wight, they knew there were pits. (I can't exactly remember how, now, but I think they may have seen the underside of the pits - where they dropped through to a lower level - before they found the topside on the upper level.)Why did they rope themselves together? They knew it had a push attack.
In the fiction, I'm happy to allow that dangling over a 30' drop might restore some clarity to the mind of even the most fearful PC! And from the metagame point of view, I don't think it would help the game to try and rob the players of their little victory. Everything else being equal, I want to encourage them to engage the gameworld and the fiction, not discourage it!Would a character genuinely fearful not slash the rope to escape?
Suppose it had been as you took it to be, and knowing that a scary foe is up ahead the PCs rope themselves together. At the table, this is the players taking steps to defend against forced movement. In the fiction, it's like Ulysses and the sirens: "I fear some of us might break when we confront the undead: but if we are roped together, then none can flee as long as one of us is steadfast!" So I still wouldn't see that as a problem.