Of course it will continue to decline, it's a free service. Only a matter of time before it's gone completely. It's already a shell of what it was only a few years ago in most markets with stations turning off OTA transmitters.
I would argue that live pro sports deals like this make cable as safe as ever.
Where is this you're talking about? In major markets, OTA transmitters aren't being turned off, they are being upgraded to state of the art digital broadcasting. The CRTC are mandating that these stations are broadcast, they aren't going anywhere soon.
Cable is dying because sports are their only property in demand. Cable subscribers who don't care about sports, at least 50%, are growing tired of subsidizing cable's most expensive product in sports programming. Once these people shed cable for other delivery methods, the price is going through the roof for the sports services.