This poem is, in some ways, a difficult one to analyze for symbols because it is full of symbols, metaphor, metonymy, allusion--every line has one or more of these. Sometimes a symbol is embedded inside a metaphor or an allusion making it even harder to sort the one from the other.
Symbols are literary or poetic elements that have a literal contextual meaning and a deeper, figurative meaning. For example, "sea" in "windings of the sea" has a literal meaning of the actual ocean with its churning, tossing, winding waves with troughs and peaks. It also is a Western cultural symbol carrying the figurative symbolic meaning of life. Thus, "windings of the sea" symbolically means the twists and turns, the up and downs, the vagaries of daily life.
Not every image, on the other hand, contains a symbol. A good example of this is "Though lovers be lost love shall not [be lost]." "Lovers" and "love" are literal without being obvious symbols of anything. A different instance, "the man in the wind and the west moon," seems to be a symbol of nothing because there is no relevant literal contextual meaning: there is no "man in the wind/moon." This personified line ("man in the ...") is best analyzed as a metaphor for nature, while "wind" and "moon" alone are often used as individual emblematic representations of nature.
Another example of the absence of symbolism in an image is "They shall have stars at elbow and foot." There is no literal way anyone can have "stars" clustering around their elbows or feet. It is a metaphor based on an allusion to Classical Mythology relating to a person taking a place among the stars upon death. "Stars" is itself a metonymy for heaven; it stands in as a substitute word for a larger concept, like "White House" is a substitute phrase for the larger concept of the American Presidency.
"Death," like "sea," is a clear symbol, though it may have more than one symbolic representation. While "death" has the literal meaning of the end of physiological life, "death" symbolizes spiritual punishment, or separation from God. "Death" also may symbolize extraordinary emotional and psychological suffering in life. It may also symbolize extreme hopelessness and despair. All of these are accepted cultural symbols for "death." Since the poem covers such wide-ranging agonies and causes of physical death, which "death" has no dominion over, I'd venture to analyze this symbol as being intended to represent every possible symbolic option: spiritual, emotional and psychological, hopelessness and despair, and cessation of spiritual being (as in, "you do nothing but die when you die").