Even if that's true, provided the bank has assets significantly greater than its obligations, it can still pay everyone back eventually with significant interest. People may be inconvenienced by not having the liquidity they expected, but they can't lose their savings. If a bank doesn't have assets that are significantly greater than its obligations, then it's undercapitalized, and the run just exposes that problem.
My point is simply that a run cannot cause depositors to lose their deposits if the bank was healthy prior to the run. Bank runs are a solved problem for everyone but banks -- a run can bankrupt the bank.
Why would a professional lender not do fractional reserve lending? Once ripple btc or usd become almost equivalent to btc/usd due to level of trust, it's easy. You will never have all customers demand their cash at the same time unless they think the lender is going under; FDIC solves that problem. I would never say that a lender is unhealthy just because they have a fractional reserve, and ripple would facilitate it.