After the Wayfarers had been away for about a year, building their guildhalls and getting their separate chapters started, Elminster once again met with them. He let them know the Mystra the Goddess of magic wanted to speak with them.
The were allowed entrance into her divine realm where she greeted them with open arms. She thanked them for all their hard work especially with restoring the great city of Rhymanthiin. This meeting however was cut short. As a black blade being wielded by the god Cyric pierced her chest. She was than enveloped in blue flame and consumed.
The plane exploded and different plane shards flew off into the depths of space. A chunk about 4 square miles that the Wayfarers were standing on remained intact and they are now unable to return home, because any normal plane shift type spell doesn’t work on this plane shard. (The reasoning is that planeshift and similar spells actually have a range, even when you can reach the outer planes, you’re travelling a certain amount of distance across the planes. Currently this shard is so far from any planes, that it simply cannot be reached.)
Elminster was able to flee just before the death of the Goddess. As the characters floated away into space they saw Cyric and Shar standing over the blue flamed burning corpse of Mystra.
Note: For those of you who might have read the books, yes, I’m working the timeline quite a bit differently. Although these events happen in Faerun, Mystra doesn’t normally die for several more years. However this works out best for the campaign so there.