Here are a few ways to rewrite this title in Swedish, depending on the style you prefer:

Most natural and common news headline in Swedish: Man i 30-årsåldern omkom i drunkningsolycka i Nyköping

Closer to the English structure (using ”after”): Man i 30-årsåldern avled efter drunkningsolycka i Nyköping

Simpler and more direct: Man i 30-årsåldern dör efter drunkningsolycka i Nyköping

Note: In Swedish news, ”omkom” (died in an accident) is the standard and most natural word to use here, and it is slightly more formal than ”dör/avled”. The phrase ”i drunkningsolycka” is more idiomatic than ”efter drunkningsolycka” in headline form, but both are correct.