Congrats for returning to Aikido !
I took about 4.5 years off from Aikido, primarily due to some knee surgeries and some other non-aikido related injuries.
I just went back to my dojo, re-signed up, and started taking class again
We don't line-up by rank where I practice, so I can't give you advice about that question. But once you've earned your shodan, it doesn't get taken away...you're just a shodan who's a bit "rusty"
The worst thing I did was stop practicing Aikido...best thing I did was to start practicing again