There should not be any impact on data-plane operations when migrating from vFMC to HA FMC appliances. The devices should continue to forward packets based on the policies stored in local running-config. VPN tunnels, inspection services etc. should all remain functional.
Obviously, you will lose control over the management plane during this period, and so if something was to go wrong and require a configuration change, then you would have to wait for the migration to finish.
Hope your migration goes well!
- BW
Please rate posts if they have been helpful.
