According to the Agile Practice Guide and the PMBOK® Guide, the primary strength of an adaptive (Agile) approach is the ability to respond to change and manage risks dynamically.

Continuous Prioritization: In adaptive environments, the backlog is not static. When a delay occurs due to an unforeseen risk, the team and the Product Owner must re-evaluate the remaining work. This involves Reprioritizing the Product Backlog to ensure that the most valuable and high-risk items are addressed immediately or deferred as necessary.

Risk-Adjusted Backlog: Agile teams use the concept of a " risk-adjusted backlog, " where work is prioritized not only by business value but also by the urgency of addressing risks. By reprioritizing, the team can focus on delivering the " Minimum Viable Product " (MVP) or the most critical features within the remaining timeframe, even if the total project duration has been impacted.

Inspect and Adapt: Rather than sticking to a rigid plan that has already been compromised, the team uses the " Inspect and Adapt " pillar. They analyze the impact of the risk and reorganize the flow of work to maximize value delivery despite the one-month delay.

Analysis of other options:

Option A: Stopping the project completely is an extreme reaction and usually unnecessary. Project management is about navigating obstacles, not abandoning the project at the first sign of a significant delay unless the business case is no longer viable.

Option B: While capturing lessons learned is a mandatory part of any project, simply " accepting the delay " without taking action to optimize the remaining work is passive and does not align with the proactive nature of project management.

Option C: Changing the delivery date to maintain the original scope is a Predictive (Waterfall) mindset. In an adaptive environment, we often prefer to keep the date fixed (timeboxing) and adjust the scope (flexibility) to ensure continuous delivery of value.

Per PMI standards, the best course of action in an adaptive project facing a disruption is to Reprioritize the work. This ensures the team remains agile, addresses the most critical needs first, and adapts the project plan to the new reality created by the identified risk.