You might be less involved with the strategic direction of a company as realized through its projects and products. That responsibility will be falling on a Product Owner and the Scrum Master is likely to spend more effort on improving delivery capability (inward vs. outward focus).
This has nothing to do with level of gratification or reward as improving one's servant leadership skills and helping a team form and grow can be as or more rewarding than influencing strategic direction for a company.
Larry, you shouldn't leave anything behind. That experience will be handy soon. It is true that moving from PM to SM require a change in behaviour. You don't need to provide direction but rather facilitate and motivate the team. In theory the self-organising team works, in practice it is hard to build a team that works without direction.
Becoming a good project manager takes time and there will always be a need for project managers. I had a SM role for a team of 47 that was in disarray when I joined. Most of the team members had a lot of experience and good technical skills but the project (ERP implementation) was not the kind of project that needed Agile and people couldn't understand the reason and benefits of using "Scrum". When you focus on cost/benefit for 10-15 years its hard to understand the benefit of 60 people sitting in a room for one day every month for "sprint planning".
Agile reached his peak and organisation start bringing back Lean practices. Have a look at SAFe and you will see what I mean. In my opinion converting PMs to full time Scrum Masters it's a waste of knowledge and skills. While I agree that all PMs should be able to perform a Scrum Master role and learn the Agile way of leading a team, there are projects that will require PMs leadership, for example when the PO is not really doing his role or in environment with strong governance. Saving Changes...