Hi Anders!
I see what you mean, but I think the logic false. It is usual to be cheered up when some future prospect is better than your current situation. The fact that there is no afterlife could be imagined to be a better prospect than one's current life if, for instance, one has an incurable disease, or is struck by grief. So you do not have to compare an idea to a fact when stating if you are cheerful or not.
And even if you do compare the idea and the fact, you can still find it fortunate that the idea is just an idea. The mind can easily make such comparisons, even though they are meaningless in the strict sense.
As I have said before, I am sad at the thought of death, simply because my mind cannot imagine what it is like to not exist, and instinctively I think it is better to exist than not to exist. Of course, once I do not exist, then I also do not prefer one state to the other, but for the moment I exist, and I definitely prefer it to stay that way.
This is something that each of us has to face, and we do it individually. Some are sad, some are cheerful, and then some look at it in a logical fashion and avoids false dilemmas.
If we go back to the "cheerfulness"-question, those who feel cheerful at the thought of death, do they also extend this cheerfulness to the death of other people, say the ones they love?