API Gateway disappeared from AWS

Do you have CloudTrail active? If not, you need to set up that service; it will provide you with all the traceability you need.

API Gateway or other components don't just disappear; they were most likely deleted.

If you don't have CloudTrail, it is impossible to know who deleted those components and when they were deleted. I recommend activating CloudTrail and rotating the credentials of all users in your account.

Ask the members of your team if they deleted the components in question.

Additionally, ensure that you follow the principle of least privilege. That will help you to minimize the potential impact of accidental or malicious actions like this one.

Have you selected the right region? API gateway is a regional service, and I believe everybody got tricked in their life by thinking of missing a resource while you were on a wrong region ;)