According to the PMBOK Guide, one of the tools and techniques for performing integrated change control is risk analysis1. This involves assessing the potential impact of a change request or a defect on the project objectives, such as scope, schedule, cost, and quality. By performing risk analysis, the project manager can evaluate the pros and cons of deploying the system with the defect, and determine the best course of action.
The other options are not appropriate, as they do not address the issue of whether to deploy the system or not.
Proposing a solution redesign, revising the quality control measurements, and developing a mitigation plan are all possible actions that could be taken after performing risk analysis, depending on the results. References:
* 1: PMBOK Guide, 6th edition, page 120