Does an indifferent creature regurgitate (or stop restraining) a swallowed opponent?

Question

Calm emotions is a fantastic spell for avoiding combat with with high CR/low Charisma opponents. One of its effects is:

Alternatively, you can make a target indifferent about creatures of your choice that it is hostile toward. This indifference ends if the target is attacked or harmed by a spell or if it witnesses any of its friends being harmed. When the spell ends, the creature becomes hostile again, unless the DM rules otherwise. (PHB 221)

As it so happens, there are several low Charisma monsters that have a swallow or engulf action. The remorhaz (CR 11, CHA 5 (-3)) is typical:

Swallow. The remorhaz makes one bite attack against a Medium or smaller creature it is grappling. If the attack hits, that creature takes the bite's damage and is swallowed, and the grapple ends. While swallowed, the creature is blinded and restrained, it has total cover against attacks and other effects outside the remorhaz, and it takes 21 (6d6) acid damage at the start of each of the remorhaz's turns.

If the remorhaz takes 30 damage or more on a single turn from a creature inside it, the remorhaz must succeed on a DC 15 Constitution saving throw at the end of that turn or regurgitate all swallowed creatures, which fall prone in a space within 10 feet oft he remorhaz. If the remorhaz dies, a swallowed creature is no longer restrained by it and can escape from the corpse using 15 feet of movement, exiting prone.

Other examples include:

• Froghemoth CR 10, CHA 5 (-3)
• Purple worm CR 15, CHA 4 (-3)

The shambling mound (CR 5, CHA 5 (-3)) has an engulf action that also blinds and restrains. Unlike the swallow attacks of the aforementioned creatures, the rules for the engulf action do not say that an engulfed creature is no longer restrained if the shambling mound dies.

Imagine the following scenario:

1. A froghemoth surprises a party and successfully bites the fighter. The fighter, who is size Medium, is automatically swallowed.
2. During round 2, the no longer surprised cleric casts calm emotions. The froghemoth fails the saving throw (by a wide margin) and is now indifferent about "creatures of your choice that it is hostile toward", including the fighter in its gullet.

The rules for what constitutes indifference primarily discuss social interaction, such as talking or persuading someone to do something or merely to leave you alone:

An indifferent creature might help or hinder the party, depending on what the creature sees as most beneficial. A creature's indifference doesn't necessarily make it standoffish or disinterested. Indifferent creatures might be polite and genial, surly and irritable, or anything in between. A successful Charisma check is necessary when the adventurers try to persuade an indifferent creature to do something. (DMG 244)

It is possible through social interaction to get a hostile creature to help you. For indifferent creatures, the worst possible outcome is "The creature offers no help but does no harm." Again, this assumes you are conversing with a creature. Assuming you have no way of communicating with the froghemoth (INT 2, does not speak or understand any languages), it seems impossible or at least highly unlikely that you could get the indifferent froghemoth to do something to help your party, but at the very least it should not harm you.

The question is, what happens when the froghemoth becomes indifferent to the fighter in its gullet?

• Does it regurgitate the fighter, because keeping the fighter in its gullet will cause harm?
• Does it stop restraining the fighter, so that the fighter can use their movement to escape?
• Does it just keep doing what it was doing, but not attack any new creatures?

Answer 1

Indifference makes no difference to a swallowed creature

There is no reason for a creature under Calm Emotions to regurgitate a swallowed fighter. The monster is already indifferent towards the swallowed fighter even without the spell, as the fighter has stopped being a threat and now is food to be digested, which is within the natural instincts of the creature. It has no attitude towards the fighter at this point, the fighter is just a meal to keep down.

There is no stopping to restrain the fighter by the creature, as being restrained is an automatic condition effect from being swallowed, it is not something the Frogemoth or Purple Worm does actively:

While swallowed, the creature is blinded and restrained

Likewise, regurgitating has nothing to do with the monster's attitude and is not a willful action. It is an automatic response that happens if the monster takes too much damage to its stomach internally. You can narratively dress this up as it throwing up whatever is down there to make the tummy pains stop:

If the remorhaz takes 30 damage or more on a single turn from a creature inside it, the remorhaz must succeed on a DC 15 Constitution saving throw at the end of that turn or regurgitate all swallowed creatures

(Ditto for the Forgemoth, on more than 20 damage, with a DC 20 Constitution saving throw).

All that being said, in the end how this should be treated should be up to your DM. See page 4, Thasha's Cauldron of Everything:

The rules of D&D cover many of the twists and turns that come up in play, but the possibilities are so vast that the rules can't cover everything. When you encounter something that the rules don't cover or if you're unsure how to interpret a rule, the DM decides how to proceed, aiming for a course that brings the most enjoyment to your whole group.

The Shambling Mound may not say that being restrained ends with its death, as the other monsters do, but this is likely just an oversight, and once it is dead, you should be able to crawl out. Again, of course, ask your DM.