If they view you as a keeper of some of the institutional knowledge that suddenly disappeared, you could give them a stopgap solution in the interim until they find a long term replacement.
If you feel confident in your standing in the organization and want to stay, you can make it clear that you understand their challenge and that you're being a team player for now, but you want to outline a clear transition plan with concrete phase-out dates so you're not stuck in a position that makes you unhappy in the long run.
I would agree with the above, but I have a few questions.
1.) Do you see yourself as a partner someday in this firm?
2.) Is the division you are being asked to help a major money maker for the firm?
3.) Do you have management skills to make changes that could fix some of the things you think should change in terms of people?
If no to #1, talk to your boss and then start looking for another job, if yes, then demonstrate you have the ability to solve the problem it will pay off in the long term.
#2 is probably a yes, or they would just shut it down and a senior partner would not have been the person running it before his passing.
#3 is tricky, but if you answered yes to #1, then forget the area of work. You can always hire people with right certifications, and instead focus on developing your management skills. If you don't want to get into management, then explain to your boss the problem, but I guess you will be gone soon. Management generally doesn't look favorably on higher salary employees that are satisfied dong what they are doing, when they obviously know you are not working to full capacity if they think you have 50+% of your time available to help them.
My thoughts, good luck!
