Key Point is Whatsapp doesn't delete an inactive account.
• What happens if my WhatsApp has been inactive for months?
• Does WhatsApp delete inactive accounts?
You can get your contacts back if you had synced them in any of the cloud service e.g. Google Account(Contacts). Sign in with your Google Account to see.
Whatsapp doesn't save your contacts name on its server.
After switching or restoring your Whatsapp account from one device to another. One can see his all groups(created or joined) but personal chats will be erased and can't be seen until you have backed up it to Google Drive and restored them at the time of account creation.
See: Restoring your chat history
After restoring your chats successfully, you will be seeing all your chats by numbers instead of names but you can now easily guess the names of acquaintances.
Or if you get your contacts saved by Google Contacts you will start to see names of the recovered chats automatically.