FSMO Role Loss implications:
Schema: The schema cannot be extended. However, in the short term no one will notice a missing Schema Master unless you plan a schema upgrade during that time.
Domain Naming: Unless you are going to run DCPROMO, then you will not miss this FSMO role.
RID: Chances are good that the existing DCs will have enough unused RIDs to last some time, unless you're building hundreds of users or computer object per week.
PDC Emulator: Will be missed soon. NT 4.0 BDCs will not be able to replicate, there will be no time synchronization in the domain, you will probably not be able to change or troubleshoot group policies and password changes will become a problem.
Infrastructure: Group memberships may be incomplete. If you only have one domain, then there will be no impact.
