Can I point my domain to my other server/space and use it till the end of the free year?
Or will the domain be voided as soon as our relationship ends?
Yes, you can cancel connectivity service and keep your account open with just DNS and Registration. Sonic pays for the first year of registration as part of the Personal Hosting deal - once that year is up, you will be charged a yearly renewal fee ($14.95 for most domains) if you choose to keep the domain active.
In order to point the domain to another provider or host, you'll need to keep DNS service, which is currently priced at $1.95/mo. The DNS records can be updated via Member Tools to point wherever you'd like.
If you'd like to keep hosting with Sonic, Personal Hosting is currently $5.95/mo for customers without an Internet connectivity product.