In the past I've occasionally allowed strong enemies to pull the rope out from below, leaving whoever is up the rope-trick stuck there unless they want to jump, or have another rope they can lower.
This is similar to what I would have done or at least along these lines.
The DM would decide that either one of the opponents knew the parameters of the spell or didn't.
If you wanted to be impartial, you could make an open Arcana roll DC 15 + 1/level of the spell.
Upon failure, have the opponents test the rope for a round, giving it a tug testing its strength, swinging it around while the ranger had a moment of reprieve while climbing, they could make ranged attacks etc. After that (next round) its anyone's game if they decide to climb up, but the decision would be how many would actually do it, and how many would continue participating in the primary fight.
If you wanted to be impartial, you could make an open Persuasion roll DC 10 with the parameters preset and known to the players. This is what I do.
Failure by 5 or more = 0
Failure by 4 or less = 1 additional orc joins
10-14 = 2 additional orcs join
15 - 18 = 3 additional Orcs + Orog join
19+ = 4 additional Orcs + 2 Orogs join
After killing and looting the ranger, they would see if it were safe to climb down and deal with the rest of the party. If not, they would stay put as long as they could, maybe even tossing the dead corpse out of their hidey-hole.
Upon success, the opponents would give chase and the same logic as above would follow, i.e. how many joined and would they stay the full hour.
Having it open and letting the dice decide usually gets you out of trouble with players and furthermore
player added input in possible outcomes, that you as DM may have never thought about, is also welcomed.