Your point is logical, however, as I see it, players being able to log out should not be accounted for at all, when it comes to deciding gameplay design.
I am not completely against BM rewards, however I disagree with a concept of a BM, that players want to participate, mainly because of rewards. I find that there is a logical fallacy in this concept, which is apparent, if you wonder what the purpose of any kind of reward is:
1) Players choose to voluntary participate in the BM in order to "get rewarded".
2) The purpose of any reward (item/perk) is survival.
3) BM is by far the most threatening event for your survival.
*Return to 1) and loop until that makes sense.*
Unless we want the BM to be a "rewarding" event just for the sake of being rewarded, which is meaningless if you think how the above loop works, the BM must be a non-optional event, in which you just have to participate and defend successfully or lose something important. It's the only way.
To account for people who 1) choose to enable the BM and later 2) log out during the BM, doesn't make a lick of sense to me, while that option exists. Unless TFP plan to send some of their pimp goons to rough up people that log out,
we should stop being concerned whether the BM can be skipped because people may decide to stop playing the game.
Let's end this "what if people quit the game" madness, especially when the BM is already optional through menu options, and focus the discussion on something that is not completely asinine.
It has 6.3 on imdb... Watching it happen in the game would probably be more entertaining.