The short version is you re-certify every two years, and during those two years you perform a set of activities like for example "Thought leadership". Certain activities gives you a specific amount of "points" which you register (and have approved by ServiceNow) to meet your minimum score within those two years. To maintain your CMA certification, you must have these maintenance points covered (and approved) by the deadline. Thought leadership is for example writing whitepapers, mentoring others, having (relevant) sessions in podcasts or videos, holding on-stage sessions (including at Knowledge) and so on. Thought Leadership considered by many CMA's to be the most difficult to maintain, but ServiceNow expects every CMA as part of that role to have those activities done by them.
Besides the Thought Leadership part, there are two other categories of maintenance - the first being working as an architect, you need to document that you are doing so by having your activities registered - and the second being a category for your own self education - for example when you take an on-demand course on Now University, these will automatically generate one point (per hour of course taken). The list of possible activities you can take to get maintenance points is specific, and shared to all CMA alumni on the alumni site.
You ask if there's a minimum standard for thought leadership, I will say "not really" - you are not validated on difficulty level or quality, but on the activity itself. Everyone has different levels.
