We have WEB application in Flex.
If I convert to EXE (standalone) my application will work affter 2020?
I need official link about this.
I'm not sure, but you may want to look into this (Adobe donated Flex to Apache) http://flex.apache.org/dev-faq.html
That's probably not an optimal plan. Operating systems change over time, and much of the work we do is around keeping up with those changes. Depending on a static execcutable to stay compatible over the long term is precarious situation, particularly if it's business-critical for you or your customers.
Here's the official link on Flash EOL:
Harman is providing services for enterprises that need Flash Player and AIR support over the long term.