Version 1.0 cost $44.99 USD so old versions Alphas 6 - 22 will be separate ?

[Morpheus]

So can I play my best version 19 forever or they will shut it down in future ?

[Roland]

If you own the game on Steam you can use the beta opt-in screen to play the older versions. It doesn't matter whether you paid a lower price or $44.99, all of the older alpha versions are included on Steam. That is not the case for any other platform. It is a Steam exclusive because they are accessed through Steam's beta feature.

TFP has said they have no plans of removing old versions so until someone says otherwise you should be able to play beloved A19 forever.