Why not just have the rewards drop from the boss rather than the after action report? Surely this would b straightforward to implement and while it wouldn't stop people who hang back to complete "...without dying" tasks it would at least put an end to afk'ers. As far as I am aware you have to be within a certain proximity when an enemy dies for it to drop anything for you so someone sitting at the start of the strike couldn't just collect their engrams from the postmaster. Marks could be awarded in the same way as glimmer drops (silken codex etc) that you then turn in to the vanguard (or -heres a great idea- your faction rep so you don't have to do pvp to buy faction gear) If I'm missing something I'd be happy to hear it but this seems the easiest solution to me.