You state, "if they run fireworks after both shows as usual?" Fireworks do not run after both shows at DL.
The usual schedule is:
9:00pm Fantasmic
9:25pm Fireworks
10:30pm Fantasmic
That said, Fantasmic's last showing is tomorrow (9/1) until it returns in November (just to not confuse anyone).
I do not know of a special Christmas version of Fantasmic. There IS a special Christmas version of the fireworks show, however: "Believe... In Holiday Magic" Fireworks Spectacular.
Also, I'd be amiss if I didn't add that NYE at Disneyland gives new meaning to the term, "Being in a can of sardines." You have never seen such crowds. Truly.