What's worth considering?
First, it's worth considering whether the experiment can reasonably be reproduced within legal and ethical boundaries. Reproducibility is a cornerstone of science, and if it's not feasible to replicate the experiment because it would be unethical or illegal, there's less value in continuing the experiment or publishing the results. Conversely, if the experiment's results can be verified within legal and ethical boundaries, this argues for a more lenient assessment. Second, consider the costs incurred by participants due to the rule violation relative to the expected benefit of continuing the experiment or allowing the use of data from the experiment. If the costs to participants were minimal, and the expected benefit to future patients from using the results is relatively significant, this argues for a more lenient assessment of the rule violation. Third, be mindful of how the costs of a sanction distribute among the various parties involved in the experiment compared to the costs for the party responsible for the rule violation. If a sanction incurs significant costs for other parties and less so for the responsible party, this argues for allowing further use of data from the experiment. Fourth, consider how a potential sanction (or the absence of one) will affect future compliance with the rules. This applies to both the individual researcher who stepped out of line and other researchers who might consider breaking the rules in the future. Fifth, consider whether participants' autonomy has been taken into account. For example, were they consulted about the use of their data (which, in itself, is a form of sanction against the researcher)? If participants have been consulted and have consented to the future use of their data, this argues for a more lenient assessment.
What can be done?