Warmaster Horus
Explorer
First, as has been pointed out you can maintain concentration on a spell no matter what the range. A few spells say you can't be on another plane is the only limitation. It's also been specifically clarified in the official sage advice compendium if you want to look....
True, there is no stated range on concentration other than some specify same plane. If you are concerned about a wizard casting Heat Metal on a 1st level PC and then teleporting to the other side of the planet, the encounter has more problems than just spell selection. At higher levels use Dispel Magic (or Counterspell it as it's being cast), break caster concentration or soak the damage and heal. Next to poison, fire is the most common damage type to have resistance and only targets metal which makes it even less useful as a general purpose spell. Certainly a nasty way to go, though. But, like, D&D, you know?