The future is never a 100% certain but that shouldn't stop us from staying optimistic. It's highly unlikely that the devs will let go of the WebGL version. WebGL is a relatively new graphics API and will see improvements over time. It's a more viable platform to sustain the 'free to play' model that FFT is known for. The Steam and WebGL servers are cross platform so you don't have to worry about players shifting over to steam.