Hi Samuel,
Obsolete means the feature is still in the product but it is not being enhanced anymore and is not eligible for technical support. We keep it in the product for backwards compatibility reasons until customers have time to migrate off the obsolete feature. So no, your project will not stop working simply by upgrading to PowerBuilder 2019 R3.
It is obsolete because we have new Web service clients to replace it that are more secure, easier to deploy, more flexible, and arguably just overall much better.
HTTPClient - this is an all-purpose HTTP client that can be used to basically do anything. You can use it to call SOAP Web services, but it will require some extra coding compared to the obsolete Web service proxy wizard. Please refer to this tech article.
RESTClient - this is a specialized HTTP client for calling REST Web APIs that return JSON result set. It requires very little coding, and can even automatically import/export JSON data from the REST Web API to a DataWindow.
Regardless the Web service proxy wizard is obsolete or not, I would immediately migrate off of that as it is not secure since it doesn't support TLS 1.2. The HTTPClient and RESTClient support TLS 1.2, and TLS 1.3 coming soon. Plus, it supports token technology such as OAuth 2.0 and JWT.
Best regards,
Armeen