The speaker of Sonnet 73 seems definitely haunted the by his own mortality, and loads the poem down with metaphors for death, like ashes, nighttime, and cold. Just to make absolutely totally sure that you didn't miss the point, Shakespeare even inserts the word "death" twice. This all sounds very depressing. Is there any sort of rosy lining? Yes, of sorts—but it won't come in the afterlife. The only solace we get comes in the closing lines, which tell us that death helps people love and cherish each other more while they are still on earth.
The speaker seems to value beauty and youth more than anything. If beauty and youth could last forever, he would be happy.
The speaker makes it sound as if he does not believe in an afterlife—love's all he needs.