Deleting Samsung account - will it delete all ST configured devices?

As my ST hub v3 turned INACTIVE after last night pushed firmware upgrade

After reading on some posts here, there is a chance deleting and recreating the Samsung account may fix the problem (although it should probably be solved by the Samsung support team that is simply not responding).

My question - is deleting/recreating the Samsung account removes all configured Z-Wave things/devices?

You should wait for support to reach out to you before deleting anything. You could end up in an unrecoverable state.