They are Restricted Free Agents, so no they don't have a contract. Had they accepted their qualifying offers, they wouldn't be going to arbitration. Leafs sending a qualifying offer to them keeps them from turning into Unrestricted Free Agents (aka Percy). Right now though, all 3 have no contracts and their rights belong to the Leafs.
If they didn't elect for arbitration, the Leafs could technically just not sign them to a contract but keep their RFA's right for the year. Plenty of examples of this in recent years like O'Reilly, Johansen, Franson, etc missing a part of training camp and the regular season because they weren't signed. Heck it happens a lot for some RFA's that go back to Europe when they aren't happy with their roles (Khokhlachev is a recent example).
With arbitration, they are almost guaranteed to be signed because they will be awarded a certain amount. None of the three will be anywhere near the threshold to allow the Leafs to walk away.