IceCube Monte Carlo studies have shown that the quality of muon and cascade reconstructions are rather resilient to permanent channel failure rates as high as 10%. (A permanent channel failure is one which cannot be repaired, e.g., a broken in-ice connector.) For muons, only the difference between the true and reconstructed space angle shows some degradation, but only by roughly 3%; for cascades there is essentially no degradation at all. These results can be extended qualitatively to tau events as well.
The main impact of such failures would be to reduce the detector sensitivity. This reduction is energy-dependent and is more pronounced at lower energies. For example, a 10% failure rate results in the loss at trigger level of 40% of muons with energies between 400 and 500 GeV, but only 5% of muons with energies between 8 and 10 TeV. Above about 30 TeV there is no loss. A 10% loss would therefore not dramatically affect ultrahigh energy muon neutrino physics, but it would adversely impact IceCube atmospheric muon neutrino physics, and the usefulness of these neutrinos as an IceCube calibration tool.
Under the reasonable assumption that sensitivity loss varies roughly linearly with the permanent failure rate, requiring the permanent channel failure rate to be below 5% reduces the impact of such losses on atmospheric muon neutrino physics. At the same time, a 5% failure rate is a realistic goal.
