If a character affected by the blue slaad's Chaos Phage disease has it cured before transformation, do they regain their HP?

Question

The description of the blue slaad's claw attack (MM, page 276) says:

While infected, the target can’t regain hit points, and its hit point maximum is reduced by 10 (3d6) every 24 hours. If the disease reduces the target’s hit point maximum to 0, the target instantly transforms into a red slaad or, if it has the ability to cast spells of 3rd level or higher, a green slaad. Only a wish spell can reverse the transformation.

This is in reference to the Blue Slaad's claw attack. The final sentence in the quote is that only a wish spell can reverse the transformation, but nothing is stated about recovering their HP. If the disease is cured before the target is transformed, do they regain their lost HP?

In addition, is the first HP loss after 24 hours or immediately?

Answer 1

The hit point maximum loss is not immediate. The character has just taken damage from the slaad's claw and failed a saving throw:

Claw. Melee Weapon Attack: +8 to hit, reach 5tf., one target. Hit: 12 (2d6 + 5) slashing damage. If the target is humanoid, it must succeed on a DC 15 Constitution save or be infected with a disease called chaos phage. While infected ...

If the damage was immediate, it would be listed as an immediate effect of the attack. Compare to the wording of similar effects that take effect immediately, such as a wight's Life Drain:

... The target must succeed on a DC 13 Constitution saving throw or its hit point maximum is reduced ...

It's up to the DM how to pace the HP max loss: it could be spread over the 24 hour period, or all at once at the instant it has been 24 (and 48, etc) hours. I've handled it by telling the character they feel really sick, and having the hit point max loss affect them after they finish their next rest.

As for reversing the HP loss:

While infected, the target can't regain hit points, and its hit point maximum is reduced ...

The reduction in maximum hit points applies while the character is infected. Once they are no longer infected, their hit point maximum goes back up to what it was before, and they can start healing up to that from their current hit points by the usual means.

Answer 2

The Wish spell cures the disease.

So it stops the health loss and the inability to regain health.

Personally, as its a disease called Chaos Phage, I'd have the player have to over come an avatar of Chaos with Health equal to that which the player lost to the disease to regain its max HP once more.