I disagree with the bolded text above.
This is been the single most important focus of my game improvement (the elimination of the downswing or risk in poker).
I have figured out how to eliminate the dreaded downswing.
My worst 500 game span is winning $2.75 per game. My worst 100 game span is still winning $0.33 per game.
So you see...my "downswings" are just winning less money than "normal."
I understand you are offering general advice on a bankroll related original question, but one should not EXPECT to lose 50 buy-ins...ever! If this is the case, you would be better off focusing on why you are experiencing so much variance and if there is anything you can do about it.
Slow and steady climbing has been the most effective way to win in MTTs (for me).