Is it possible to restore an expired transient?

If you are coding this, probably the best approach is not to use the transient for the value you are displaying, but a normal custom field that’s updated .

In that situation you have the transients, which will time-out and trigger the request. The result you get is checked by your code and then stored elsewhere.

You can use that field to display it on the front at all times. Whenever a transient request completes you update that field.