Another option, if the sentence ends in a period, is to press F8, then ".",
and tap the Delete key.
F8 is the Extend Selection key. Among other things, after pressing F8, Word
will extend the selection up to the next character you type. So, F8? extends
up to the next question mark, F8) extends up to the next ), and so on.
Pressing the Delete key or Backspace key deletes whatever is selected and
turns Extend Selection off (the Esc turns Extend Selection off, but doesn't
de-select whatever's currently selected, without deleting anything).
In addition, pressing F8 multiple times selects the following:
2x: whole current word
3x: whole current sentence
4x: whole current paragraph
5x: whole current document section (which is the whole document if it
contains a single section)
6x: whole document (if multi-section)