Just for context, the CDM bridge allows you to call CDM from DSM.
But ofcourse this adds complexity and should in my opinion only be used as an intermediate solution and as an exception.
The default approach would be to indeed migrate over fully and decommission CDM. Specifically for the CDM logic there is no automated migration given the differences between CDM and DSM logic. Typically it also makes sense to do some level of redesign as DSM can be a lot more compact - in some cases really an order of magnitude less components - because of it's ability to run across lists of propositions, and in general improved expressiveness. Pega can provide some examples based on your existing CDM logic what this could look like, contact your AE. You can typically readily reuse your entire data infrastructure.