So i am assuming you have not lost your access, but you are wondering what happens if you do.
1. If you lock your self out of your portal, lets say by accident you enable conditional access on all Users incorrectly. In this case you will have to contact Microsoft support using a Global Customer Service phone number.
2. Portal.azure.com is backed by all regions. In the event something should happen to the datacenter your are using, you would just have to wait for Microsoft to resolve the issue. You could insure you application spans multiple data centers, but i would not suggest this unless you truly can not survive a data center down scenario for a few hours.
3. You can create custom roles for the portal that will allow your staff different rights, like read permissions to troubleshoot your services, reboot services etc. These custom roles can also be granted permission to allow creating support cases.