How the custom changes and functionality will affected after MS changes take place place?

Hello 

I would like to know that in SharePoint Online, How the custom changes and functionality will be retain during MS changes take place.

We have created some custom component based on SP List object using Azure Services. 

I may be wrong, i heard that sometime after Office 365 updates, some time you need to re-deploy or need to update the component or code of the component. 

Is there any guideline or Best Practices available on this?

Regards

Avian