The regular expression:

(?i-msx:\b(?:deceased|passed\s+away|died|dying|death(?!\s+benefits))\b)

matches as follows:
  
NODE                     EXPLANATION
----------------------------------------------------------------------
(?i-msx:                 group, but do not capture (case-insensitive)
                         (with ^ and $ matching normally) (with . not
                         matching \n) (matching whitespace and #
                         normally):
----------------------------------------------------------------------
  \b                       the boundary between a word char (\w) and
                           something that is not a word char
----------------------------------------------------------------------
  (?:                      group, but do not capture:
----------------------------------------------------------------------
    deceased                 'deceased'
----------------------------------------------------------------------
   |                        OR
----------------------------------------------------------------------
    passed                   'passed'
----------------------------------------------------------------------
    \s+                      whitespace (\n, \r, \t, \f, and " ") (1
                             or more times (matching the most amount
                             possible))
----------------------------------------------------------------------
    away                     'away'
----------------------------------------------------------------------
   |                        OR
----------------------------------------------------------------------
    died                     'died'
----------------------------------------------------------------------
   |                        OR
----------------------------------------------------------------------
    dying                    'dying'
----------------------------------------------------------------------
   |                        OR
----------------------------------------------------------------------
    death                    'death'
----------------------------------------------------------------------
    (?!                      look ahead to see if there is not:
----------------------------------------------------------------------
      \s+                      whitespace (\n, \r, \t, \f, and " ")
                               (1 or more times (matching the most
                               amount possible))
----------------------------------------------------------------------
      benefits                 'benefits'
----------------------------------------------------------------------
    )                        end of look-ahead
----------------------------------------------------------------------
  )                        end of grouping
----------------------------------------------------------------------
  \b                       the boundary between a word char (\w) and
                           something that is not a word char
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------