re: My mentor and best work friend announced his retirement today

Nobody knows everything. You're obviously young. Mentors aren't necessarily people in your direct line of work. Figure out where you think you need to grow/learn and go find someone that excels in those areas. My guess is you'll be surprised and enriched by establishing a few of those relationships. I don't have a mentor per se but I have several business owners in related businesses that I keep in touch with on a regular basis. I just pick their brain and get advice on broad and specific topics. It's motivating/inspiring to me to be around other driven and successful people. Give it a go.