Flexor the Mighty!
18/100 Strength!
If the PC's are not interested in your plot hook I'd just drop it. I'm not going to end a campaign over the players not following a potential hook. If its that big a deal you need to ram them in the face with it, and make sure they are interested in playing that kind of campaign.
Saying "well you ignored my Lord of the Rings hook because you really wanted to be Fafhrd and the Grey Mouser and adventure for riches and glory..so boom game over suckers! You should have been the type of PC I wanted in my story." No thanks.
If you are dropping hooks and letting them sandbox it why put in hooks that if they ignore will screw up the game? Otherwise just base the entire campaign around it and make sure they have to follow it. The game world really is there for a fun environment for the characters to explore and murderhobo in, and taking the living world too far will mess things up.
Saying "well you ignored my Lord of the Rings hook because you really wanted to be Fafhrd and the Grey Mouser and adventure for riches and glory..so boom game over suckers! You should have been the type of PC I wanted in my story." No thanks.
If you are dropping hooks and letting them sandbox it why put in hooks that if they ignore will screw up the game? Otherwise just base the entire campaign around it and make sure they have to follow it. The game world really is there for a fun environment for the characters to explore and murderhobo in, and taking the living world too far will mess things up.