The impacts are usually partial. For example, scaling is impacted but everything already deployed contributes to work up to capacity. Or, you can't change configuration but the previous configuration works as configured. Often surprisingly not so impactful even if there can be limited work stoppage.
The problem with the us-east-1 outage is that a lot of big companies are there, so even if you try your best not to depend on us-east-1, your third party providers are most likely there. In my previous company, we were completely down during us-east-1 outage because of other dependencies that are beyond our control.
Entirely fair. I have thus far avoided that problem. Not always engineering's choice.