Don't panic until it happens.
That sort of thing is very difficult to stop. The result isn't really worth the time, energy, and money that it would take them to effectively stop fansubbing.
Of course, they're pretty dumb for even suggesting this in the first place. It would be worse for them if they succeeded.
No free methods of watching anime -> not as many people watch anime and the ones that do only watch what's shown on television and the rare case of watching one because of a good promo (buying a $25 DVD because of a promo is a tough sell for sure) -> no word of mouth -> the only cue that the R1 industry has on what to license are their gut feelings + people that previously both watched fansubs and helped support the R1 industry don't know what to buy because they didn't get to watch them for free first + the people that didn't watch fansubs don't know what to watch anymore because the people that previously told them what was worth their time don't watch anime anymore -> the R1 companies get confused + people stop buying because they don't know what to buy -> R1 industry collapses -> Everybody loses
Not a smart chain of events to set off.