If we are in an AI centric world of course we should allow AI to finish work by dead artists. In music a lot of the time if an artist dies their label whom has control over their catalogue will often release unfinished, unpolished posthumous albums/music. If one is able to polish their art with AI and finish while still respecting the artists vision it is better to do rather than not release or release unfinished.

I wouldn't call it "guessing" to finishing a work that is already started. You can look at the work already finished and any plans at how the work would finish and than make a decent inference based on the knowledge of the artist vision. A dead artist can say yes or no if they're able, before they day, it can also be implied that an artist would want their final work finished and released. If an artist would want their art released after they die and AI can help with I think we ought to do so.

1) If it just "feels off" to you than you aren't making a rational argument you're making an emotional one, you've already decided you're opinion and than backtrack to make an argument to lead up to it. 2) If a painter where to leave a rough sketch, an AI wouldn't just "guess" it would look at the painters other works, take in all the data and finishing the painting how the painter would seem to finish such a project.