The way i think he see's it is being alive = activly supported by the original devloper. dead = devs doesnt care anyore about that title.
Keeping that perspective in view, yes sometime when that happens, the devloper will only release bugfixes, but some other game that are open to modding from the get go still receive heavy support from the devs, Space Pirate and Zombies is a good decent example for this and the very best example i can find relate to that would be the X series, even if the game was open to modding from the get go ( no steam, but in-game script editor ), they kept providing content, patches, adding new commands to the script editor to help the community.
As for the workshop only thing, i dont know, i never really used it to be honest, the only time i did in fact was with torchlight 2, all other games are modded/patched by hand sine im an old school modder. Workshop is simply a mod database tool providing ease of use to the player.
Hell Prison architect is in alpha and sports the workshop, are you saying the game is dead? because it is not and its being heavily worked on.
This discussion is a little bit useless in my book because there will always be example for both side of the argument, games are like ppl, you cant tell the personality of that guy just by one action.