Simpson Thacher's PE problem: How lean can a firm go?

The article reports that departure of Simpson Thacher & Bartlett's former London, England head Greg Conway to the US symbolizes several shifts in the firm's London office. It states that his move has marked another exit from Simpson Thacher's private equity practice in the City, and mentions the three London departures, namely Mike Wolfson, Alvaro Membrillera and Conway.