The only way I can see of defeating it would be if your characters have freedom of movement. It can grapple high level characters as well as low, and after a few strenght drains.
I ran Forge of Fury and removed it in fear of the group's tendancy to not negotiate, especially with non humanoids. A few months later I played in a game and came across one with our 17th level party. It was a screwy 'low magic' campaing an the party had no magic items, and the wizard had his spell book stolen. Regardless, it would have been a tpk, but as me (the cleric) and the wizard watched the monk, fighter and rogue get drained to 0 str, I decided to use out of chacacter knowlege to negotiate with it. The DM didn't know they were intelligent until he looked it up at the table, and was reluctant to negotiate, but it was that or a 3/5 party kill.
I'm not familiar with the history of the roper, or what they were thinking, but unless the DM has it sing golum's fishing song as it's eating the party, there's little chance they would think to negotiate with it.