Dimensional Grappler

[Ogadim]

It doesn't seem like this mythic hero ability has been discussed on this site from the searches I've done, so I will just have to bring this question to bear.

Here are the relevant parts of the scenario: A mythic Purple Worm with the Dimensional Grappler ability (details in spoiler below) has a Hamatula currently grappled in its mouth. When the Hamatula's turn comes up, it attempts to use its Greater Teleport ability to escape. With a caster level of 12, spell level of 7, and INT modifier of +1, would the DC of the worm's Will save be 18 (10 + spell level + modifier)? If the worm succeeds at this save to identify the spell/intended location and chooses to prevent it, how long does the Dimensional Anchor effect last? If it is a persistent effect, would it last for 16 minutes (# of worm hit dice * 1 min/level) and does it only prevent the currently grappled enemy from teleporting away or any enemy grappled in its mouth for the duration?

Dimensional Grappler:

Dimensional Grappler (Su): When you have an opponent grappled or pinned and it attempts to use a teleportation effect, you can attempt a Will save against the effect, even if it would not normally allow a save. If you succeed, you learn the type of teleportation effect (such as dimension door) and the creature's intended destination, and then may prevent the effect (as if using a quickened dimensional anchor, using your character level as your caster level) or accompany the opponent as if you were part of its gear with negligible weight.

[Drake Brimstone]

As per Dimensional Anchor it would last 1 min/level for that target, even if it leaves the Worm's mouth. It has essentially been targeted with a quickened Dimensional Anchor spell.

[Ogadim]

Drake Brimstone wrote:

As per Dimensional Anchor it would last 1 min/level for that target, even if it leaves the Worm's mouth. It has essentially been targeted with a quickened Dimensional Anchor spell.

Ok. So if the worm makes its Will save, it can choose to either a) cause a quickened Dimensional Anchor effect cutting off transportation for 16 minutes from that target or b) it allows the effect and transports with it but the target would be able to transport again next round barring another save?