If the eCard design is no longer available, you cannot make a template from that sent eCard. However, you can create a new eCard with the same message text, signature, colors etc. and select a new eCard design. You can then create a template from that eCard.
Important Note: CorpNote occasionally retires older eCard and invitation designs. Retired eCards are still able to be seen in your account and any links to a sent eCards will still work properly.