I strongly disagree, there was substantial evidence - provided in the game- that he could extend his life if he chose to, and there was very good reasons that he would have chosen to pursue these things when romanced. I consider what happened to Thane as something similar to Solas being forced to die alone in future content, which would be horrible.
I am also totally confident that the reason his ending was forced into one outcome was about saving resources rather than doing his story justice (not helped by the fact that his original writer had left BIoware in the meantime). The same can be said for Jacob.
What they did to players who had romanced Jacob is off the scale in WTFFFFFFFFFFFFFFFFFFFFFFFF?? Was that supposed to be entertaining? seriously? It is like they should have released it on 1st April bad.
Also, why is it the sick guy who has to die? that's a total cop out as well, if they're going to go that way, why not forced death for everyone? Why didn't they make it so Garrus died no matter what? or Liara? that would have been a right laugh.
As you can probably tell, I was very annoyed by ME3 and thinking about still gets me riled, I trusted that BW would do good by all of their fans, but in their effort to save money and appear edgy the messed it right up. I'd have been happier with just some letters from Thane saying he was getting a Lung transplant etc etc, and one from Jacob where he was on an important mission - would have been better than what we got IMHO. For those who didn't romance them, the content could have been as it was.
I will be annoyed if anything like this happens to Solas, and I am hopeful that it won't, but I know not to fully trust in BW to honour previous character arcs after ME3.