VSTS PAT used for Build Agent expires, now what?

When using Visual Studio Team Services (VSTS) and Build/Release Agents, the way to authenticate is through Personal Access Tokens (PAT). A PAT can either expire in 90 days, 180 days or 1 year. The question is: what happens after expiration with my Build/Release Agent? Will it stop working? What if I restart it after expiration?