I really think they are going to revert to New England Patriot thinking. As players are getting closer to signing big deals, if the Astros can't sign them to a hometown discount by before their last season, I see them being shipped out for prospects to keep the farm system going. Dallas Keuchel will be the first one. He is a free agent after 2018. If they can't get him to sign on the dotted line, I would not be shocked to see the Astros trade him before the season started so they could get a maximum amount of prospects for him. They already have several pitchers in their farm system that are a year or two away from coming up.
I think they do everything they can to keep Altuve (he signed a "security" deal until 2020) , but he has Boras as an agent, and the Astros have not done well with old Scott. Think of the haul Altuve could bring in. Fans would be pissed, but if you keep winning like the Patriots do, it might not matter as much.
Luhnow has shown he loves his prospects, and knows how to get the good ones. If he keeps bringing up new guys, and signs free agents as needed like he did this last offseason, I think he can keep these guys competitive for a long time.