There are a couple of things to consider here.
For your personal penalty, if you have not been making a habit of afk-ing games, 1 afk game will not even give you a warning let alone LPQ so no worries about that. If you do have high leaver meter, then getting put into LPQ may not be worth it. Personal call.
For the trolls, if you leave game, you will lose the ability to report them after match. You can probably submit a support ticket there after, but the most surefire way is to report them after match and that means endure the game.
Personally, I would play the game out maybe go practice cs-ing. I main support so my cs-ing skill is pretty weak. Every troll game I play is a practice game for when I have to play another role, but that's just me. I would play the game out and report them after match, make sure to leave a descriptive details of what happened in the comment and submit a support ticket follow up. If it gets to the point that I can't even practice cs-ing, I would just stand in a safe spot, minimize League, go watch a youtube vid and make sure to move every 3,4 minutes so the client wont' force close. Yes, I will get hit with leavebuster even doing that, but I will not lose the ability to report them after match.