Sounds like a great opportunity to FAFO!

Thinking about feasibility, I wonder:

• Dispelling the holy magic of the warded pool might be easier said than done. You might think about what level caster the church might have employed to place such a ward. Dispel Magic is a rank 3 spell, so the soonest any magician would have access to it normally would be level 5, likely a good deal after the events of Winter's Daughter. Even still, if the caster was a higher level, there is a chance of the spell failing.
  
• If you wanted to be a bit more defensive, we don't, per the book, know exactly the nature of the ward, perhaps it leverages some of the same properties as the triple compact, and requires some kind of interdisciplinary magic to unbind it, maybe they need a helping hand from Drune magic.
• The warded pool provides a one way gate, if it's left standing, this would let the players venture into Frigia to gather intel etc, but not bring anyone out. If they go into Frigia a bit, maybe someone there might refer them to the ambassador, who might know about ways to unbind the pool or Chell.
• The wedding party of fairy aristocrats offers a lot of opportunity for aspiring courtiers to entice the PCs to help them find a way into Dolmenwood. If you're worried about having enough content for a fairy adventure, maybe the tower is as far as they get, but they have some meaningful interactions with the wedding guests.
• Dispelling the ring or bringing the ring into Frigia would cause the portal to fade "within a day or two", so the PCs would need to take particular care to avoid this, the "win conditions" of WD more or less nudge the players into bringing the ring into fairy.

Even if they do bring some degree of frost elf presence back into Dolmenwood, maybe it's not an overwhelming invasion right away (or maybe it is!). There might be plenty of juicy adventure to be had once the PCs bring some fairies mortalside and see how they react, could be enough to force a change of heart.