I think a lot of places will either no longer have a royal patron or there will be next to no engagements with them. Charles has slimmed down the working royals and there is no feasible way for them to split the patronages and make them all a priority.
I agree. The late QEII and DoE had so many patronages/charities/organizations that a decade or so might pass by before they could attend an in person event. Also I believe that many organizations are opting to merge with larger ones for financial reasons or have closed over time. Charles will now have state duties to attend to that require his presence. Regarding the redistribution of the patronages/charities etc...that were formerly attached to QEII and the DoE, I believe that the following will occur in the coming months.
Organizations, charities and patronages that are largely associated with the monarch will naturally pass to KCIII.
The same can be said for those related to Cornwall and Wales will likely be taken over by William.
Edward still has the Duke of Edinburgh Prize and all activities associated with it.
The remaining ones that still desire a royal patron will ultimately be added for the monarch and the working royals.