I hate the proverbial bus. It seems to assume that central employees should be completely dispensible.
If a key employee, being the architect or even the CEO, is hit by a bus, the company will take a hit. If employees are a central, strategic assets, you can't go around killing them off and expecting no impact on your business. Deal with it.
The important metric is whether the company/project can recover, if it is resilient. Just because one guy drives the decisions, it doesn't mean that the team filling in the details don't know the code and the motivations behind it, and there can't be a guy from that team who could take a promotion, or that the team couldn't be reasonably productive for a while, while a new architect is brought on.
In short, stakeholders should always be concerned with the potential discontinuity of (especially high) performance. But it's rather like technical debt (or any other kind); something that should be managed rather than avoided at all cost.
If a key employee, being the architect or even the CEO, is hit by a bus, the company will take a hit. If employees are a central, strategic assets, you can't go around killing them off and expecting no impact on your business. Deal with it.
The important metric is whether the company/project can recover, if it is resilient. Just because one guy drives the decisions, it doesn't mean that the team filling in the details don't know the code and the motivations behind it, and there can't be a guy from that team who could take a promotion, or that the team couldn't be reasonably productive for a while, while a new architect is brought on.