Brian was the better half of Radha. SPRT is no IBM or Cisco with plenty of talent to fill in the gap. SPRT is a struggling company with an Enterprise Business(~50% of revenue) that continues to deteriorate going against the big fish and suite vendors.
Not sure how good Brian's replacement is but institutional investors invest in strong Management teams. Brian's departure is a net negative. IMO Brian was more valuable to SPRT than Radha.
The only security blanket left for investors is the cash hoard investors have awarded this company through secondary offering. Investors have had ZERO return on their investment.
Synopsys maybe bigger and better company, but if the future was so bright for SPRT Brian would not have left.