If Monero were to cease development, how would Kovri I2P keep up with changes to the I2P protocol? Would use of Kovri be able to be routed around?
Kovri and Monero are 2 distinct stand-alone projects that does not share any source code in common. Even if developers are not the same, it is still the same community (they are both under https://github.com/monero-project, same funding system ). So while there is nothing technically that would prevent Kovri to continue if Monero were to cease, it is highly unlikely that it will happen in the current state of things.
However, the goal IS to build a project and a community that can sustain itself.
From what I have observed on Reddit and Slack, the Monero and Kovri developers aren't the same people. While these projects are working closely together, I don't think the goal is for Kovri to depend (solely) on Monero. I would recommend to ask your question directly in the #kovri-dev Slack channel, and post the feedback here as an answer.