Finishing off lost mines of phandelver

[Gubbster]

I'm relatively new to D&D and I am dming a group of three through the campaign. I planned that after the players complete their quest they will be approached by a traveling merchant and offered to draw cards from the deck of many things. Has anyone else done anything fun afterwards or just have the player's keep their characters. I feel that the deck of many things could either make a very happy, or sad ending to the story.

[Gastronomie]

The Deck of Many Things is a truly, truly trollish item. It could be fun, but it could also possibly spoil the fun, depending on what happens. It'll be more "outrageous" rather than "sad" if the characters, as a reward for all their good adventuring, suddenly got slaughted, or imprisoned into a pocket dimension, or lost all of their magic items. S*** happens with the deck.

I dunno, you could always connect it to other published adventurers. Making the Black Spider a cultist of Tiamat or a scout of the Drow can lead to either Hoard of the Dragon Queen or Out of the Abyss, respectively. Fleshing out relationships with the NPCs the party especially liked could be another option.

Treasures. If the Black Spider had an entire spellbook, that's a great present for the party wizard. Perhaps the Warlock in the party gets an extra invocation from his/her Patron in exchange for doing its bidding (if the quest had anything to do with the patron). The rogue might get further connections with underground organizations. The sort.

But really, whatever works best for your players.