I haven't done the math yet, but I think making periodic withdrawals while winning is like having insurance.  At the end of the day, it's very possible and likely that a series of future bets will be continuous losses until zero.  The question is whether you can withdraw more than your initial principal before that happens.

From my own experience, I have been able to double my bitcoin more often than I hit a losing streak and lose everything.  Definitely not fail safe, but that is a bit less risky to me than regular martingale.