We all ship TootTooth, but Toot seems to be making absolutely no progress in winning Lacuna over. I doubt Jim is going to leave this minor plot unresolved, the readers enjoy it to much and Jim appears to have a savage glee in making James Marsters voice Toot and Lacuna.
So how can it be resolved. Looking at the characters development and the world of the Dresdenverse, I can think of only one possibility where Lacuna accepts Toots advances.
Toot kills Dracula.
Now hear me out. Readers deduced that Lacuna was a Tooth Fairy, confirmed by WOJ and in Battle Ground where Lacuna expressed obsessive interest in the teeth of the fallen. My own personal theory is that she was detailed to scrimshaw the teeth of Lloyd Slate whilst he was still alive, it seems very her style.
Therefore the thing most likely to attract the attention of Lacuna is teeth, and who is the owner of the most notorious teeth in the Dresdenverse?
Dracula.
Now Harry is set up for conflict with the Black Court following the events of Battle Ground, and during that conflict Toot attacked and beat Mavra, a Senior Black Court Vampire, perhaps foreshadowing him taking on Mavra’s sire himself.
It is therefore not improbable that at some point in accompanying Harry on the destruction of the Black Court Toot kills Dracula and removes his upper canine teeth or ‘fangs’ to present to Lacuna to make matching his and hers necklaces as a symbol of love.
Lacuna would never let one of a pair of the most prized teeth in creation out of her possession, and so will agree to Toots advances (but probably with notions of divorce or murder) to get the remaining Tooth.