Part of an ongoing series of 5e (2014) Rules notes.  See the end of the post for notes on 5.5e (2024) rules.

The range and need of line-of-sight is pretty clear when spells are initially cast, but what happens if range is exceeded or line of sight is broken in a spell that lasts more than an instantaneous effect — in particular, with spells that require Concentration to maintain them?

(In the case that came up in my campaign, the party wanted to maintain a spell as they fled; a more common instance is the affected party fleeing the caster and breaking LoS or exceeding distance.)

The General Rule

It’s pretty straightforward:  range and line-of-sight don’t matter once the spell has been cast. As PHB 203 puts it:

Once a spell is cast, its effects aren’t limited by its range, unless the spell’s description says otherwise.

So, as a general rule (and as confirmed by Jeremy Crawford and also confirmed by Jeremy Crawford), once you have successfully cast a spell on a spot or a target opponent, it will continue until it naturally ends (i.e., with a Concentration spell, until the time limit is passed or the character drops concentration), regardless of what the range or line-of-sight is. You are maintaining the spell, not the targeting.

Spells that say otherwise, of course, are otherwise (the specific overrides the general).

That said, if you and the target are beyond LoS, you don’t know what is going on there. Maybe the guy you threw Heat Metal on ran into the next room, took off the armor, and put it on an orphan waif, and your continuing the damage is killing an innocent. Ah, well …

What about in 5.5e (2024)?

The basics still look pretty much the same. The notes on spell range say:

If a spell has movable effects, they aren’t restricted by its range unless the spell’s description says otherwise.

Which kind of looks close to what was there before. It clearly encompasses spells that are described as moving (e.g., Flaming Sphere). Does that also include spells cast on a target that then moves away? What about the other way around — if the spell is cast on a fixed spot (or unmoving target) and the spell caster moves?

They would seem to apply from previous precedent, and because some spells explicitly in their description that they fade or end when a given range is exceeded (e.g., Mage Hand).

Similarly, from a line of sight perspective, the only mention is in the initial spell casting:

A Clear Path to the Target. To target something with a spell, a caster must have a clear path to it, so it can’t be behind Total Cover.

No mention is made of lingering effects after that, so, presumably, the same is true: a clear path is only needed during the initial casting (targeting).

Finally, the Sage Advice Compendium notes the following:

If you’re concentrating on a spell, do you need to maintain line of sight with the spell’s target or the spell’s effect?

You don’t need to be within line of sight or within range to maintain Concentration on a spell unless a spell’s description or other game feature says otherwise.

Those are the only rules or rulings on this that I can find for 5.5e. As things change and/or are pointed out to me, I’ll update this entry.