What happens if an old domain redirecting to a new domain expires? Will it still redirect? What is the effect on search engine ranking?
Lets take these on one at a time.
Q: What happens if an old domain redirecting to a new domain expires?
A: The old domain ceases to exist at all.
Q: Will it still redirect?
A: No. The domain no longer exists.
Q: What is the effect on search engine ranking?
A: That depends. For example, if there are a number of links to the old domain, these links will become broken and the value of the links being passed from the old domain to the new would no longer exist.
If the old domain holds no value, for example little to no user traffic or link value, then it may be wise to let the old domain go. This is not something we can determine. Only you can assess this.
What happens if an old domain redirecting to a new domain expires?
Expirations of domain names can not be seriously discussed without knowing at least the TLD, and even better the full domain itself to know its sponsoring registrar.
Registry and registrar rules and custom procedures vary by TLD.
Typically, a domain expiring can exhibit the following behaviors (on or after the date of expiration):
- stop resolving at all
- having nameservers changed and hence redirecting access to a page at registrar showing the domain to be expired and needs to be payed
- being put in auction
At least in the first 2 cases it will stop being redirected as it was previsouly.
All of this can impact its "SEO", and leave marks in its history with consequences for the future.