Is it not a grief to the death when a companion and friend turns to enmity?: The implied answer to this rhetorical question is “Yes.” Good News Translation rephrases the question as a statement. Another possible approach is:

• When a close friend becomes an enemy, the sorrow it causes is almost enough to kill you.

Quoted with permission from Bullard, Roger A. and Hatton, Howard A. A Handbook on Sirach. (UBS Helps for Translators). New York: UBS, 2008. For this and other handbooks for translators see here.