D&D 5E Question on using dispel magic against a summoned and planar bound demon.

[ECMO3]

I refer you to the bolded section of the Planar Binding Spell.

"Concentration" is the duration on Summon Greater Demon.

The duration is extended from:
"Concentration, up to 1 Hour" - duration specified by Summon Greater Demon

to:
"24 Hours" - duration specified by planar binding (with further extension on a higher level slot).

 

[kigmatzomat]

Not as far as I can tell, dispel only affects one spell.

Dispel Magic definitely affects multiple spells (emphasis mine)

Choose one creature, object, or magical effect within range. Any spell of 3rd level or lower on the target ends. For each spell of 4th level or higher on the target, make an ability check using your spellcasting ability....

 

[UngainlyTitan]

"Concentration" is the duration on Summon Greater Demon.

The duration is extended from:
"Concentration, up to 1 Hour" - duration specified by Summon Greater Demon

to:
"24 Hours" - duration specified by planar binding (with further extension on a higher level slot).

Yes, and that implies that the summons is still running unless the caster has dropped concentration.

 

[ECMO3]

Yes, and that implies that the summons is still running unless the caster has dropped concentration.

The summons is extended, but concentration is no longer the duration of the spell any longer. Concentration is the actual duration of the spell, that is what is extended by Planar binding. It works exactly like a higher level casting of bestow curse where the duration changes from concentration to a fixed amount of time.

It is also worth noting you can not send the demon (or other summons) back by ending concentration once you cast planar binding and there is no option to end the planar binding early. Once you cast it the creature is bound until the planar binding ends.

There is also a logical falacy to this interpretation - If planar binding lasts 24 hours ..... and the spell is extended to the duration of planar binding (24 hours), and then if the spell ends before 24 hours because you lost concentration ..... then it was in fact it was not extended to the duration of the planar binding.

Finally it is impossible to concentrate while unconscious, so if this were true you could not even use planar binding for 180 days like it says you can on a 8th level casting, because you would need to sleep and could not remain conscious that entire time.

 

[UngainlyTitan]

The summons is extended, but concentration is no longer the duration of the spell any longer. Concentration is the actual duration of the spell, that is what is extended by Planar binding. It works exactly like a higher level casting of bestow curse where the duration changes from concentration to a fixed amount of time.

It is also worth noting you can not send the demon (or other summons) back by ending concentration once you cast planar binding and there is no option to end the planar binding early. Once you cast it the creature is bound until the planar binding ends.

There is also a logical falacy to this interpretation - If planar binding lasts 24 hours ..... and the spell is extended to the duration of planar binding (24 hours), and then if the spell ends before 24 hours because you lost concentration ..... then it was in fact it was not extended to the duration of the planar binding.

Finally it is impossible to concentrate while unconscious, so if this were true you could not even use planar binding for 180 days like it says you can on a 8th level casting, because you would need to sleep and could not remain conscious that entire time.

Yes and I do not disagree with any of that. But it is not what I am trying to say.
So, Fred cast Sumon Demon and then casts Planar Ally. Ben rolls up a turn later and casts Dispel Magic and dispels the Planar Ally, my position, is that unless Fred has dropped concentration on the Summon Monster then Summon Monster is still running and Fred has control of the demon.

Now I do agree that if Fred has gone asleep then he is not concentrating on the Summon and thus the Dispel on the Planar Ally removes control of the Demon as per the Planar Ally rules.